TM 750-254 Cooling Systems Tactical Vehicles 1972

8/9/2019 TM 750-254 Cooling Systems Tactical Vehicles 1972

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TM 750-254

TECHNICAL MANUAL

C O O L I N G S Y S T E M S :

T A C T I C A L V E H I C L E S

This reprint includes all changes ineffect at the time of publication -Changes 1 and 2.

HEADQUARTERS, DEPARTMENT OF THE ARMY

29 MARCH 1972


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WARNING

There is danger to personnel from hot blowing solder. Wear safety goggles, rubber gloves and rubber apron while blowing solder.

WARNING

If hot cleaning vat solution, muriatic acid or flux enters the eyes, wash generously for 15 minutes with clean water. Seekmedical attention.

WARNING

When working with the hot cleaning vat, safety goggles, rubber shoes, rubber apron and gloves should be worn forprotection against hot vat solution.

WARNING

Flux, caustic solutions and cleaning acids can cause skin irritation. Wash Immediately with soap and clean water. If theskin comes in contact with these.

WARNING

The operating pressure of cooling systems is being progressively increased and some exceed 15 psi When testing apressures of more than 15 psi, the push-on rubber caps and plugs may blow off. To prevent this danger, clamps or wiresshould be used for holding these plugs or caps firmly.

WARNING

Do not under any circumstances mix cleaning compound with antifreeze compound or corrosion inhibitor compound.Never mix the and cleaning compound before putting It into the cooling system. Do not spill compound on skin, clothingor painted portions of the vehicle. If spilled, flush with clean water Immediately.

WARNING

The radiator cap should be turned to the “vent" position before removing, to allow escape of hot steam that might causepersonal injury.


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*TM 750-254C2

Change HEADQUARTERSDEPARTMENT OF THE ARMY

No. 2 WASHINGTON, D. C., 3 April 1973

COOLING SYSTEMS: TACTICAL VEHICLES:

TM 750-254, 29 March 1972, is changed as follows:Page 2-4 . Add to Table 2-1 the following entry:

Reference

Item FSN Fig Para* Use Fig Item

No No No No

TESTER, Battery and 6630-105-1418 2-29g Testing coolant protection, 2-26.1 N/Aantifreeze degrees Fahrenheit

Page 2-24 . Add the following subparagraph:2-29g. Use of Battery/Antifreeze Tester (FSN 6630-105-1418). To use this instrument which is available throughnormal supply channels, place a few drops of coolant on

the clean measuring window, close the cover and sightthrough the eyepiece. The graph should have a distincshadow edge across it. See figures 2-26.1 and 2-26.2

Figure 2-26.1. Antifreeze and battery tester 1


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Figure 2-26.2. Antifreeze and battery tester scale

By Order of the Secretary of the Army:

CREIGHTON W. ABRAMSGeneral, United States Army

Official: Chief of Staff

VERNE L. BOWERS

Major General, United States Army The Adjutant General

To be distributed in accordance with DA Form 12-38, (qty rqr block No. 250) Organizational maintenance requirements foTruck, Utility 1/4-Ton, M151.

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TM 750-254

C-1

Change HEADQUARTERSDEPARTMENT OF THE ARMY

No. 1 Washington, D.C., 31 October 1972

COOLING SYSTEMS:

TACTICAL VEHICLES

TM 750-254, 29 March 1972, is changed as follows:

Page I. Add the following statement at the top of the page:

"This annual contains copyright material, used by permission of Inland Manufacturing Company."

By Order of the Secretary of the Army:

CREIGHTON W. ABRAMSGeneral, United States Army

Official: Chief of Staff

VERNE L. BOWERSMajor General, United States ArmyThe Adjutant General

Distributions:

To be distributed in accordance with DA Form 12-38 (qty rqr Block No. 250) organizational maintenance requirements foTruck, Utility, 1/4 Ton, M151.


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*TM 750-254

TECHNICAL MANUAL HEADQUARTERS,DEPARTMENT OF THE ARMY

No. 750-254 WASHINGTON, D.C., 29 March 1972

COOLING SYSTEMS:

TACTICAL VEHICLES

CHAPTER 1. INTRODUCTION Paragraph Page

Section I. General..............................................................................................................1-1 1-1II. Components of cooling system .........................................................................1-4 1-1

III. Inter-relation of cooling system and other engine systems .............................1-20 1-10

CHAPTER 2. MAINTENANCE OF COOLING SYSTEM

Section I. Special tools and equipment .............................................................................2-1 2-1II. Preventive maintenance....................................................................................2-3 2-4

III. Troubleshooting............................................................................................. ..2-23 2-19IV. Coolant ............................................................................................................2-25 2-20

CHAPTER 3. REPAIR OF RADIATOR

Section I. Radiator construction.........................................................................................3-1 3-1II. Radiator cleaning...............................................................................................3-6 3-3

III. Testing............................................................................................................3-16 3-6IV. Repair ..............................................................................................................3-26 3-10V. Repair of aluminum radiators ..........................................................................3-41 3-20

INDEX ALPHABETICAL INDEX......................................................................................... I-1

*This manual supersedes TM 9-2858,8 May 1945 including all changes, and TM 10-4150, SECTION V 21 November 1941

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CHAPTER 1INTRODUCTION

Section I. GENERAL

1-1. Scope

This manual contains maintenance instructions for alllevels of maintenance on cooling systems for tactical

vehicle engines. Liquid-cooled engines are the primarysubject of these instructions.

1-2. Forms and Records

a. Authorized Forms Maintenance forms andrecords that you are required to use are explained in TM38-750.

b. Recording . At the completion of the coolingsystem processing, the condition of the cooling systemand the degree of freeze protection shall be recorded onDA Form 2408-1, Equipment Daily or Monthly Log or DAForm 2409.

c. Field Report of Accidents . The reports necessary

to comply with the requirements of the Army safetyprogram are prescribed in detail in AR 385-750.

d. Equipment Improvement Recommendations.

Deficiencies detected in the equipment or materials shouldbe reported using the Equipment ImprovemenRecommendation section of DA Form 2407. Foinstructions on the use of this form, refer to TM 38-750

Submit the completed DA Form 2407 to CommandingGeneral, U. S Army Tank-Automotive Command, ATTNAMSTA-ME, Warren, MI 48090.

1-3. Reporting of Equipment PublicationImprovements

The reporting of errors, omissions, and recommendationsfor improving this publication by the individual user isencouraged Reports should be submitted on DA Form2028 (Recommended Changes to publications) andforwarded direct to Commanding General U S Army Tank-Automotive Command, ATTN AMSTA-MAP, Warren, M48090 A reply will be furnished directly to you.

Section II. COMPONENTS OF COOLING SYSTEM

1-4. General

Cooling systems are made up of many individualcomponents These operate in close association with eachother to enable the engine to produce its power efficientlyReduced performance or failure of any one of thesecomponents will require servicing or repairing to restore

engine performance to normal requirements The followingillustration (fig 1-1) establishes a nomenclature for thesetypical components and shows their approximate locationin a typical automotive cooling system In the illustration,the engine block and cylinder heads contain coolantpassages which comprise the water jacket.

These passages are designed so that the coolant isdistributed in the proper proportions for efficient coolingEngine block castings have holes in the lower portion othe block These holes provide openings to the watepassages and are necessary for removing the filler andwhen the block is cast The holes are sealed by disks

which are known as core hole plugs. Plugs offer someprotection against block cracking when coolant waterfreezes These plugs occasionally leak Small leaks can bedetected by anti-freeze residue and calcium depositsaround the plug. Leaky core plugs should always bereplaced.

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1 Inlet 11 Heater line2 Fan 12 Radiator hoses3 Drive belt 13 Oil cooler line4 Radiator overflow tank 14 Hose clamps5 Overflow tank pressure cap 15 Outlet6 Thermostat 16 Radiator drain cock7 Heater line 17 Radiator core8 Engine block drain plug 18 0verflow tube9 Core hole plug 19 Radiator tank

10 Water pump

Figure 1-1. Typical cooling system components

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1-5. Drive Belts and Shafts

a. Belts (fig 1-2). The most common type of fanand water pump drive makes use of a single belt which isdriven by a pulley on the engine crankshaft Normally, thisbelt also drives the generator. Other vehicles may haveseparate belts for one or two of these units, or two belts todrive a single unit In any case, proper operation of thewater pump drive belt is the most critical. When the waterpump stops during engine operation, overheating of theengine follows almost immediately. Belts stretch inservice, adjustment of belt tension is by movablemountings on one or more units driven by the belt.

b. Shafts Some heavy-duty engines make use of ashaft to drive the water pump Such a shaft is usuallydriven from the engine crankshaft or camshaft by gears.The shaft often drives the generator as well as the waterpump Flexible couplings are installed In drive shafts tokeep them properly lined up in their bearings.

Figure 1-2. Fan, shroud and drive belt.

1-6. Pipes, Hoses and Connections

The purpose of connection hoses and pipes is to isolatethe radiator from engine vibrations and to provide a leakproof path for adequate coolant circulation through thecooling system components. Hoses are attached to thevarious necks and flanges by clamps. Clamps may besnap-on spring wires, screw type adjustable clampsflange and gasket bolt-on joints or "O" rings. Leaks thaare discovered at the hose clamp can often be repaired bytightening when they are of the adjustable screw or bolflange type.

1-7. Miscellaneous Fittings

a. Drain Cocks (fig 1-3) There is always a draincock or removable screw-type plug located at the bottomtank of the radiator or at the outlet to permit draining ofcoolant. Similar points of drainage are provided for theengine block. In some systems, there will be a drain cockor plug in the pump housing if it Is the lowest point in thesystem. For complete draining of all parts of the system

every coolant drain plug must be removed and every draincock opened.

Figure 1-3. Cooling system drain cocks

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b. Steam Escape and Recirculation Tubes. Someoverhead valve engines have a coolant tube connectingthe rear end of the cylinder head with top tank of theradiator, which allows escape of steam from the water

jacket without causing overflow loss. Coolant flowsthrough this tube into the radiator even with thermostatvalve closed, to prevent overcooling of the engine duringcold weather, the tube is equipped with a shut-off valvethat can be closed. In another design, the tube from the

rear of the cylinder head is connected into the thermostatby-pass of that coolant flowing in the tube is recirculated inthe water jacket without entering radiator.

c. Core Hole Plugs In practically all engine water jackets will be found a number of round openings whichare sealed by metal plugs driven into the holes. Theseopenings in the outside walls of the cylinder block orcylinder head are necessary in the casting process, butperform no cooling system function. The core hole plugswhich close these openings often incorrectly called "freezeplugs" or "frost plugs". Although core hole plugs may beforced out by a solid freeze-up In the water jacket, they are

not a safety device which can be depended on for theprevention of freeze-cracking damage in the engine.

d. Other Fittings . In some engines a cover plate orside plate is used to close a large opening on the side ofthe cylinder block water jacket. One type of cover plate isconstructed with passages and outlet holes to provide fordistribution of coolant in a manner similar to that of thewater distribution tube. A few cooling systems have morethan one water outlet from the cylinder head and use anassembly of metal piping called a "water manifold" to carrythe coolant to the radiator.

1-8. Fan and Shroud(Fig 1-2).

a. Fan . Operation of the fan pulls a large volume ofair through the radiator core Besides removing heat fromthe radiator, this flow of air also provides some direct aircooling of the engine The fan provides most of the air flowthrough the radiator at low road speeds when the forwardmotion of the vehicle forces comparatively little air throughthe core Reducing the size of the drive pulley increasesthe speed of the fan For operation in extremely hotclimates, larger fans and smaller pulleys are sometimesinstalled.

b. Shroud . Military vehicles are generally equippedwith a tunnel-like structure around and behind the fancalled a shroud The purpose of the shroud is to direct theflow of air for most effective cooling. Some vehicles haveair baffles on the front side of the radiator to direct air flowthrough the core.

1-9. Radiator(Fig 1-4).

a. General The usual radiator assembly consists oa radiator core with a top tank and a bottom tank In somedesigns, the tanks may be located on the sides of thecores. The top, or inlet tank contains an outside pipecalled the radiator inlet and usually has a coolant baffleinside and above, or at the inlet opening The radiator filleneck is generally attached to the upper part of the top tankand has an outlet to the overflow pipe The bottom tankalso has opening which is called the radiator outlet Refe

to Chapter 3 for repair of radiator.

Figure 1-4. Radiator

b. Function of Tanks . The top tank collectsincoming coolant and distributes it across the top of theradiator core The baffle in the top tank assists indistributing coolant to water tubes and also preventscoolant from being thrown out of the radiator. Theoverflow pipe provides an opening from the radiator foescape of coolant or steam that otherwise might causeexcessive pressure in the cooling system. The bottomtank collects coolant flowing from the core and dischargesit through the radiator outlet.

c. Core Construction Practically all military coolingsystems have tubular radiator cores which consist of a

large number of vertical water tubes and many horizontaair fins around the tubes. Water passages in the tubes areusually very narrow, and the tube itself is made of very thinmetal

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d. Core Function In the radiator core, a largeamount of heat is rapidly transferred from the cool ant intothe air. Through the water tubes, the flow of coolant isdivided into many small streams which causes a smallamount of cooling liquid to be exposed to a comparativelylarge cooling surface in the tubes. This results in rapidflow of heat from the coolant to the tubes and air fins Heatis carried away from the tubes and fins by the air movingthrough the core

1-10. Radiator Pressure Cap(Fig 1-5)a. General . The radiator pressure cap contains two

spring-loaded normally closed valves. The larger valve iscalled the pressure valve and the smaller one is called thevacuum valve. A shoulder in the radiator filler neckprovides a seat for the bottom of the cap assembly and agasket on this seat prevents leakage between the cap andthe filler neck. By closing off the overflow pipe opening,the pressure cap prevents overflow loss of coolant duringnormal operation. It also allows a certain amount ofpressure to develop within the system which raises the

boiling point of the coolant and permits the engine tooperate at higher temperatures without coolant overflowfrom boiling.

Figure 1-5. Radiator pressure cap - cross-sectional view.

b. Function (1) Pressure valve The pressure valve acts as a

safety valve to relieve extra pressure within the system. Inthe majority of transport vehicles, the pressure valvesopen at about 4 pounds per square inch. When the valve

is forced open, it allows steam and coolant to escapethrough the overflow pipe until the pressure drops belowits opening point. Four pounds pressure in the coolingsystem will prevent overflow loss from boiling of water until

a coolant temperature of about 225°F (at sea level) is

reached. Some vehicles have valves with openingpressures as high as 17 pounds This pressure raises the

boiling point of water to about 255°F.

(2) Vacuum-valves The vacuum valve opens onlywhen pressure within the cooling system drops belowoutside air pressure as the engine cools down. Higheoutside pressure then forces the valves open, which allowsair to enter the system by way of the overflow pipe. Whenpressure inside and outside again becomes approximatelythe same the vacuum valve closes. This automatic actionof the vacuum valve prevents collapse of hose and othe

thin-walled parts of the cooling system without internasupport.

c. Operation of Pressure System (1) When a system is equipped with a pressure cap

it is generally referred to as a pressure-cooling systemThe radiator used in such a system is especially designedto withstand extra pressure. Tightness of all connectionsand joints is particularly important since pressure naturallyaggravates any existing leakage. An airtight coolingsystem is necessary to obtain the benefits of pressurecooling.

(2) Except under the heaviest driving conditions or inextremely hot weather, most military engines can beoperated without pressure in the systems. However, insome vehicles normal operating temperature is alwaysabove the boiling point of the coolant. Proper functioningof the pressure-cooling system is absolutely necessary toavoid large overflow losses of coolant from boiling, evenunder average operating conditions.

1-11. Radiator Overflow Tank(Fig 1-6)a. General. Radiator overflow tanks, sometimes

called surge tanks or expansion tanks, are standard

equipment for some vehicles. They are Installed on othevehicles as special equipment for operation in hot or drycountry. The overflow tank serves as a receptacle focoolant overflowing from the radiator and provides for itsreturn to the system. Thus, the overflow tank conservescoolant and reduces the need for frequent filling of theradiator.

b. Construction. Overflow tanks may vary incapacity from 2 quarts to a gallon or more. They areusually mounted fairly high with reference to the coolingsystem. The bottom of the tank is connected to theradiator overflow pipe through a metal tube which isusually connected by short pieces of flexible hose. When

the cooling system is equipped with an overflow tank, thepressure cap is placed on the tank rather than on theradiator, and a plain cap is used on the radiator. This caparrangement leaves the overflow pipe open to the tankThe plain cap on the radiator must always be pressure-tight to permit

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the tank to operate properly. Most tanks are equipped withan overflow pipe and drain cock.

c. Operation. Either expansion of the coolant whenit is heated or steam pressure due to boiling will forcecoolant into the overflow tank. Boiling may occur duringoperation, but it happens more often after the engine isstopped. When the engine cools down, pressure in thesystem drops below the pressure of air outside and any

coolant held in the overflow tank is forced back into theradiator. The overflow tank prevents loss of coolant fromboiling during periods of severe vehicle operation.However, if the overflow from the radiator is so great thatthe tank is filled, coolant will be lost through the tankoverflow.

Figure 1-6. Radiator overflow tank.

CLOSED

1-12. Thermostat

a. General . Full-length engine water jackets, largeefficient radiator cores, and rapid coolant circulation in thesystem provide the extra cooling required for engineoperation under heavy load in hot weather. Howeverunder lighter engine load in cool weather, the sameamount of cooling would remove too much heat from theengine. Therefore, the amount of heat removed from theengine must be controlled for different operating conditionsand air temperatures. This is done by the thermostawhich regulates engine temperature by automaticallycontrolling the amount of coolant flowing through theradiator core.

b. Construction

(1) Bellows-type The thermostat (fig. 1-7) consistsof a valve and a heat-operated unit which moves the valveThis type of thermostat-operating unit contains a specialiquid designed to boil at a certain temperature. When thatemperature Is reached, the boiling liquid creates gas

pressure which expands the bellows and opens thethermostat valve. When the liquid cools and condensespressure is reduced, allowing the bellows to contract andclose the valve.

(2) Coil spring-Type In this type of thermostat (fig 1-8), the valve is operated by a bimetallic coil which dependsfor its operation upon the difference of coefficients oexpansion of the two metals. The coil expands and opensthe valve when heated above a certain temperature. Asthe coil cools down, it contracts and closes the valve

Figure 1-7. Bellows-type thermostat - cutaway view.

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1-13. Water Pump

a. General . Every modern cooling system has awater pump to circulate the coolant in the system. Thepump, which is usually located on the front or side of theengine block, receives coolant from the bottom of theradiator and forces it through the water jacket into theradiator top tank.

b. General Construction The water pump is acentrifugal-type pump, having an impeller with bladeswhich force the coolant outward as the impeller rotates.The impeller is located in a pump housing and is mountedon a shaft which runs on one or more bearings. The shaftis driven by the engine through a belt or a shaft (para 1-5).The fact that the impeller is submerged in the coolant butmust be driven from outside of the cooling system, createsthe problem of sealing the impeller shaft against leakage.The water pump shaft seal is the only moving water joint inthe cooling system.

c. Packless Type . The most commonly used type

of pump on military vehicles is the nonadjustable packlesstype. The packless pump has a built-in, self-adjustingseal. Individual pumps vary somewhat in seal materialsand arrangement of assembly. Some packless pumps areprelubricated when assembled, but others require periodiclubrication.

1-14. Cylinder Head Joint

a. Water Transfer Ports . The coolant flows fromcylinder block up into cylinder head through passagescalled water transfer ports The lower part of each passageis in the block, and the upper parts is In the head. A tight

seal in the joint between the two parts of these waterpassages is very important.

b. Cylinder Head Gasket (fig 1-10) The joints in thenumerous water transfer ports, as well as the combustionchamber joints, are all sealed with one large gasket calledthe cylinder head gasket. To obtain the tightest possibleseal in these joints, the openings in the gasket, whichmatch the water transfer ports and combustion chamberopenings, are reinforced with metal eyelets described asgrommets. The head gasket has a double duty toperform; it must seal the extreme pressures of combustionwithin the cylinders and at the same time maintainleakproof coolant joints at the water transfer ports. To be

specific, the cylinder head gasket must preventcombustion gas leakage to the outside of the engine,between cylinders, and into the water passages, it mustalso prevent coolant leakage outside the engine, and tothe cylinders of the engine. Proper uniform tightness ofthe cylinder head bolts is necessary to maintain aleakproof head gasket joint.

Figure 1-10. Liquid and gas joints in cylinder head gasket

1-15. Engine Water Jacket

a. Construction The water passages in the cylindeblock and cylinder head form the engine water jacket Inthe cylinder block, the water jacket completely surroundsall cylinders along their full length. Within the jacketnarrow water passages are provided between cylinders focoolant circulation around them. In addition, watepassages are provided around the valve seats and otherhot parts of the cylinder block. In the cylinder head, the

water jacket covers the combustion chambers at the top othe cylinders and contains water passages around thevalve seats when the valves are located in the head.

b. Function and Operation (fig. 1-11). Passages othe water jacket are designed to control circulation ofcoolant and provide proper cooling throughout the engineWaste heat flows directly to the coolant through metawalls of the combustion chambers and cylinders. Heaabsorbed by the pistons passes into the coolant by way othe cylinder wall. The heat in the valves flows to thecoolant through the valve seats and guides. Since

exhaust valves may run as hot as 2,000°F (yellow-red

heat), proper cooling around the exhaust valve seat is ospecial Importance.

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Figure 1-11. Circulation of coolant in engine water jacket.

1-16. Engine Temperature Gage(Fig 1-12)

a. General . The engine temperature gage providesa convenient means for checking engine-operatingtemperatures. There are two principal parts in theassembly, the gage unit and the temperature sensing unit.

b. Gage Unit The gage unit mounted on theinstrument panel and connected to the temperaturesensing unit registers the temperature of coolantsurrounding the engine unit.

Figure 1-12. Engine temperature gage.

c. Temperature Sensing Unit The temperaturesensing unit is mounted in direct contact with the enginecoolant and is usually located at the rear of the engine.

1-17. Water Distribution Tube

a. General . Some engines, particularly L-head

types, have a water distribution tube in the water jacketextending from the water pump to rear end of engineThis long, flat, thin-walled tube has an opening at one endfacing the pump outlet and a number of outlet openingsalong one side facing the water passages around theexhaust valves.

b. Function (fig 1-13) The water distribution tubereceives coolant from the pump and delivers it throughspaced outlet openings directly to the hottest parts of theengine, such as the exhaust valve seats. The tube isremovable, but the water pump must first be taken ofbefore the tube can be reached In order to draw the tube

completely out of the water jacket, the radiator must alsobe taken out.

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Figure 1-13. Coolant flow through water distribution tube in engine water jacket.

c. Other Coolant Distributing Devices . Some valvein-head engines have small water nozzles or jets built intothe cylinder head to direct the flow of coolant towardexhaust valve seats. Other systems use built-in plates obaffles to direct coolant circulation in the water jacket.

1-18. Shutters, Screens, Etc.

Brush guards, air inlet screens, or similar attachmentsmay have no direct connection with the cooling systemand may be entirely for protective purposes; however, theyall restrict the flow of air through the radiator andtherefore, must be considered In connection with enginecooling. Improperly adjusted shutters or clogged air inlescreens may reduce air flow so much that cooling capacityof the system can be seriously affected.

1-19. Gaskets

When two flat surfaces are bolted together to confine aliquid under pressure, they are usually sealed with agasket In automotive cooling systems, gaskets are used

between flanges which house the thermostat. They arealso used between water pump flanges and in bolt-on typeradiator tanks. See 1-14 Cylinder Head Gasket.

Section III. INTER-RELATION OF COOLING SYSTEM AND OTHER ENGINE SYSTEMS

1-20. General

Separate circulating systems may be connected to theengine cooling system to provide cooling for auxiliaryengines and air compressors. In some cases temperatureregulation for a chassis unit, such as transmission, is

provided by circulating engine coolant through the unit.

1-21. Engine Lubricating System

The cooling system and lubricating system are dependenton each other for proper operation. Flow of lubricating oilassists in keeping the engine at proper operatingtemperatures by transferring part of the waste heat frompistons to cylinder walls and by removing the heat frombearings. In addition, the oil reduces waste heat fromfriction by properly lubricating the moving parts. On theother hand, satisfactory lubrication depends on proper

operation of the cooling system. If the coolant fails toremove its share of waste heat, excessive metatemperatures may reduce or destroy the lubricating valueof the oil. Excessive heat may also cause chemicachanges in the oil which produce sludge, "varnish," andother harmful deposits. Overcooling also interferes with

proper lubrication.

1-22. Other Engine Accessory Systems

a. General In a number of ways, the operation ofthe cooling system affects and is affected by the operationof other engine accessory systems.

b. Fuel System . Overcooling wastes fuel andoverheating may cause vapor lock Conversely, animproper mixture of fuel and air raises the coolant

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CHAPTER 2

MAINTENANCE OF COOLING SYSTEM

Section I. SPECIAL TOOLS AND EQUIPMENT

2-1. Tools and Equipment

Standard and commonly used tools and equipment having

general application to this materiel are authorized for issueby tables of allowances and tables of organization andequipment.

2-2. Special Tools and Equipment

All special tools and equipment are listed for requisition In

the pertinent parts manual. Table 2-1 contains only thosespecial tools and equipment necessary to perform theoperations described in this technical manual, It isincluded for information only and is not to be used as abasis for requisitions.

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Figure 2-1. Special tools and equipment (sheet 1 of 2)

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Table 2-1. Special Tools, Test, and Support, Equipment

Reference

Item FSN or Use Fig.No.

ItemNo.

Reference No. Fig

No.

Para No.

TESTER: thermostat 2-7a Temperature control thermostat andindicator

2-1 1

TESTER: coolingsystem 2-9d, 3-22 Test radiator caps 2-1 2

TESTER: flo 4910-015-2395 2-17d, 3-18a Test for radiator blockage 2-1 3GUN: flushing 4910-449-6790 3-8b Cleaning radiator and engine block 2-1 4TESTER: combustion 3-21e Test for combustion leakage 2-1 5VAT: cleaning 3-9b Cleaning radiator 2-1 6BOOTH: spray 4940-078-4126 3-8a , 3-14 Painting and flushing radiator, 2-1 7STAND: radiator test 4910-078-9190 3-42e Radiator testing and repair 2-1 8PRESS: arbor 3444-449-7295 3-39a Straightening radiator cores 2-1 9TOOL cleaning 2815-494-8257 2-22, 2-15a Removing debris from radiator cooler

fins.

2-1 10

SET: plug 4910-273-3660 3-19d Radiator testing 2-1 11

Section II. PREVENTIVE MAINTENANCE

2-3. Generala . Cooling system preventive maintenance avoids

engine-cooling failures, operating difficulties, and loss ofequipment use. Neglect of cooling system preventivemaintenance services often results in avoidable work,expense, and time required for corrective repairs andreplacements. Tools or replacement parts are not alwaysreadily available for emergency corrective services, and

engine-cooling failures may occur In situations when it isInconvenient or even impossible to perform correctiverepair work. However, the most serious penalty forneglecting cooling system preventive maintenanceservices are operating difficulties, loss of mobility, failure ofmission and the serious effect such failure may have oncritical military operations,

b . Practically all cooling system troubles can bedetected by the driver in their early stages before theyseriously affect vehicle operation and they are still easy tocorrect. For the stationary engine operator or driver thetwo most important indications are coolant operating

temperature and coolant level. Therefore, preventivemaintenance services to the cooling system should beconcentrated on these two first requirements. While allother preventive maintenance services, such as checks forleakage or defective mechanical condition of parts, arealso necessary, these conditions are nearly alwaysindicated by the engine temperature gage, by level of thecoolant in the radiator, or by both.

2-4. Engine Cooling Problems in MilitaryOperationSpecial requirements of military engines and severeconditions of transport and combat operation make Inecessary that the engine cooling system be maintainedas closely as possible to maximum efficiency at all timesMany military-vehicles are powered with comparativelylarge engines which develop proportionately large

amounts of heat that must be carried off. Also, cooling isoften made more difficult by the presence of air flowobstructions necessary for protection. Weather conditionsfrom the heat of the desert to the bitter cold of the ArcticPower requirements, which range from emergency highspeeds on surfaced roads to heavy uphill hauling throughdeep mud, add further to the problem of engine coolingAt the same time, military operating conditions, severeshocks, vibration, flying debris, sand and dust. exposureand accidental and combat damage, cause rapiddeterioration of the cooling system and loss of coolingefficiency. To keep the cooling system constantly in repaiand in best working order requires the most carefu

attention to periodic preventive maintenance services bythe organizational mechanic.

2-5. Leakagea. Causes Leakage is probably more common in

the vehicle cooling system than In any other liquid-carryingunit, due to the stresses and strains set up in joints andconnections by wide changes In coolant and metatemperatures, especially during cold-weather operationEngine vibration, road

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shock, and deterioration of gaskets, and wear, breakage,or corrosion of metal parts may create leakage; theseconditions are often more severe in military operation.The radiator pressure cap, which is used on nearly allmilitary vehicles, creates additional pressure in the system,thereby increasing the leakage tendency at hoseconnections and other water joints. Radiator leakage maybe caused by accidental damage to the core from flyingstones and debris, minor collisions with other vehicles or

objects, or from sabotage and combat damage. Suchdamage can easily occur without the driver’s knowledge.

b. Appearance and Effects Small coolant leaks,which show dampness or even dripping when cold, maynot be noticed when the engine is hot, due to rapidevaporation of the leakage. Leakage of antifreezecompound may be easier to find because It evaporatesmuch more slowly than water. Rusty or grayish-whitestains at joints in the radiator or engine water jacket (fig 2-2) are usually indications of leakage, even though thereappears to be no dampness. Even small leaks should notbe neglected, since they often become larger, sometimes

suddenly, and generally while the vehicle is being driven.When a driver neglects leakage inspection he risksoverheating during operation, possible mechanicalbreakdown, and failure of his mission.

Figure 2-2. Outside leakage of engine water jacket.

2-6. Rubber Hose

Leaks are more common at radiator hose connectionsthan anywhere else In the cooling system. Enginevibration has a tendency to wear and loosen rubber hoseconnections. Clamps may buckle the hose and threads onthe clamp bolt are sometimes stripped. The hose itselfhas a limited service life. Heat and water cause hoseswelling, hardening, cracking, and rotting. Deterioration of

hose usually takes place more rapidly from the inside (fig2-3) so that outside inspection is not dependableHardening of old hose increases the difficulty of keepingconnections leakproof. Hose failures not only result inleakage, but may also cause restriction of coolancirculation through clogging or collapsing. Rubbeparticles from rotted hose linings will clog the radiatowater tubes and are very difficult to remove. Rotted hosemay break open without warning and cause a large

coolant losses. In addition to the usual radiator hosesome military vehicles have other coolant hose and tubessuch as the cylinder head water by-pass and steam reliefand overflow tank tubes. Frequent outside examination oall hose and connections and careful inside inspection ofradiator hose whenever the connections are openedrequire little time and can save much trouble

Figure 2-3. Inside deterioration and clogging of rubber hose.

2-7. Thermostat

a. Causes of Failure The function and operation othe thermostat is such that this indispensable unit does nohave an indefinite service life and can fail with little or no

advance warning. The valve and operating mechanism Issubjected to extreme temperature changes, corrosion, andalso to wear and bending movement. Rust or foreignmatter in the coolant interferes with proper thermostaoperation and overheating from any cause may damage itDefective thermostats may stick open or closed, or theymay leak. Thermostat Testers (1, fig 2-1) are availableand will prove to be a time-saver. To test, remove thethermostat from the vehicle. Place thermostat in testerallow to heat and read the thermostat openingtemperature.

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Figure 2-4. Bellows-type thermostat.

b. Effects of Failure Automatic control of engineoperating temperatures provided by the thermostat Isabsolutely necessary (summer and winter) for efficientengine performance. If valve fails to close properly, theengine will run too cool; then sludge formation and otherharmful effects of overcooling can take place (para 2-18e).If valve fails to open properly, engine temperature will riseand overheating difficulties may follow. Engines should

not be operated with thermostat removed, except In caseof emergency.

c. Temperature Gage Check on Thermostat Operation The temperature gage should be observedduring engine warm-up and on road tests in order to besure thermostat is functioning properly. Whenever gagecontinually indicates unsafe low or high temperatures,thermostat should be removed and tested.

2-8. Fan and Drive Belts

a. Fan and Shroud Military vehicle operation often

requires high engine output at comparatively low vehiclespeeds. Under these conditions, the amount of engineheat increases faster than the natural flow of air throughradiator resulting from movement of vehicle. Thereforeadequate engine cooling must depend on forced air draftof the fan. Fan efficiency is even more important instationary engines and in military vehicles having armorscreens, and other restrictions to air flow. Bent fan bladesor a loose, bent, misalined, or damaged fan shroud

interferes with proper air flow and reduces coolingPeriodic Inspection and servicing of the fan and shroudassembly Is essential to proper engine cooling.

b. Drive Belts Preventive maintenance of the fandrive belt is also of first importance, because this belusually drives both fan, water pump and often thegenerator. Continuous flexing, friction, and heat cause fanbelt cracking, friction, wear, and deterioration. Looseadjustment may result in slippage, rapid belt wear, and anoverheated engine. Overtight adjustment also sears thebelt and causes early failure of shafts and bearings. Infan, water pump, or generator. A neglected fan belt may

break without warning and cause sudden overheating andoperating difficulties. Therefore, inspection of fan belcondition and adjustment should never be neglectedClose examination is necessary to discover small flawsparticularly since belts usually begin to crack through frominside. Immediate replacement of doubtful fan belts isgood insurance against vehicle failure during operation.

2-9. Radiator Pressure Cap(Fig 2-5).a. Importance of Proper Operation . The radiato

pressure cap has more effect on cooling system operationthan is generally realized. A properly operating pressure

cap increases the normal margin of safety betweencoolant operating temperature and boiling point from 5°F

to 17°F on transport vehicles and as high as 50°F on some

combat vehicles. This additional margin of safety helps toprevent boiling during operation in hot weather, at highaltitudes, and under heavy load.

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Figure 2-5. Radiator caps, plain - and pressure-type.

b. Causes of Failure The radiator cap is subjectedto high coolant temperature which cause relatively rapid

deterioration of the gasket. The valves and underside ofthe cap are exposed to extremely corrosive effects of hotsteam and air in the upper radiator tank. Since the cap islocated above normal liquid level, it receives littleprotection from rust inhibitors in the coolant (para 2-32),with the result that cap and valves may fall from corrosiondamage. Even a small amount of rust scale or dirt willinterfere with operation of pressure and vacuum valves.Frequent removal and replacement of radiator cap forcoolant level observation increases the possibility ofleakage and pressure loss, due to wear of gasket and cap-locking mechanism.

c. Effects of Failure An air leak above liquid level in

the radiator, such as at cap gasket or pressure valve, willprevent pressure from building up, and benefits of thepressure cap will be lost. Coolant may boil in somecooling systems even at normal operating temperatures ifthe cap is not pressure-tight. If the pressure valve fails toopen, sufficient pressure may build up in the system tobreak radiator seams or blow off hose connections.Failure of vacuum valve to open when system cools maycause collapse of hose and other parts which have nointernal support.

WARNINGThe radiator cap should be turned to the "vent"

position before removing, to allow escape of hot

steam that might cause personal injury.

d. Handling and Maintenance To avoid damage tocap gasket and gasket seat on filler neck, care should beexercised in removing and replacing cap. When fillingradiator, metal filling spouts or nozzles should not beallowed to come in contact with filler neck gasket seatProper maintenance consists of daily inspection of gapseat, and gasket, and periodic cleaning of cap and valveschecking of valve operation, and testing for tightness ofvalves and cap seal (2, fig. 2-1).

2-10. Radiator

a. Leakage and Failure (fig 2-6) Engine vibrationand road shocks put a strain on all radiator seams and

joints that may lead to breakage and leakage, particularlyin water tubes, tanks, and outlet and inlet fittingsAdditional strain is set up by extreme changes In metatemperatures, especially during cold-weather operationCross-country driving over rough terrain multiplies theeffects of ordinary shock and vibration. Neglect of smaleaks may result in complete radiator failure, excessiveleakage, rust clogging, and over-heating difficulties. Thusit is extremely important to keep the radiator mountingproperly adjusted and tight at all times, and to detect andcorrect promptly even the smallest leaks.

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Figure 2-6. Radiator leakage.

b. Air Passage Obstruction . The primary function ofthe radiator is to transfer heat efficiently from the coolantto the air (para 1-9d). This is not possible without clean,straight air fins and unobstructed air passages. Flyingdust, sand, grass, leaves, and other debris may clog airpassages in a very short time. Air fins are easily bent anddamaged by impact of small stones and from otheraccidental causes. The problem of maintaining sufficientair flow through the radiator is often further complicated bybrush guards, air inlet screens, shutters, armor, etc.Therefore, constant attention to the condition of all airpassages and restrictions is required in order to avoid thedanger of overheating. In extreme cases, cleaning may berequired at least daily.

2-11. Radiator Overflow Tank

a. Function The radiator overflow tank serves astemporary reservoir for coolant overflowing from theradiator while driving, or Immediately after the engine isstopped. Any coolant collected in the tank is forced backinto the radiator when the engine cools down and createsa vacuum in the cooling system (para 1-9)(fig 1-6).

b. Causes of Failure. Like the radiator cap, theoverflow tank is exposed to corrosive effects of steam andair. Being empty most of the time, it receives littleprotection from rust inhibitors in the coolant. Thin-walledsteel overflow tanks may therefore rust through from theinside and allow coolant overflow to leak out and becomelost. Water, condensed in the tube connecting pithradiator, may freeze or the tube may become clogged withforeign matter.

c. Effects of Failure . An air leak in tank-to-radiatotube or above liquid level in the radiator can cause failureof the vacuum and prevent coolant in tank from returningto the radiator. In fact, a liquid or air leak anywhere in the

cooling system will make overflow tank operation lesseffective. Clogging of connecting tube not only puts tankout of service but also seals the system, creating thepossibility of harmful pressures.

d. Prevention of Failure . Proper functioning ooverflow tank depends on maintaining an airtight coolingsystem, and free unobstructed flow between tank andradiator. This requires frequent inspection for coolanleakage, for air leaks above coolant level, for connectingtube clogging, and for presence of coolant in overflow tankwith engine cold.

2-12. Water Pump

a. Pumping Failure The water pump is the onlypower-driven unit in the coolant system. Pumping failuresare most often caused by broken or loose drive belts, buedge wear of impeller blades and wear of pump housingalso reduce pumping capacity. Sand, rust, and otheabrasive foreign matter in coolant have a tendency to cleaareas impeller blades. Corrosion of impeller (fig 2-7) andhousing may result from failure to install corrosion inhibitowith water, or to discard rusts antifreeze solution.

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Figure 2-7. Corrosion of water pump impeller.

CAUTIONOperation of engine with coolant frozen may shearoff the impeller pin and leave impeller loose onshaft, or cause slippage of pump belt drive thatwould burn belt at the driving pulley.

b. Leakage (figs 2-8, 2-9) Leakage is a morecommon trouble than pumping failure. The pump housing

joint is under strain from the pump drive and may corkloose and leak if the mounting bolts are not kept tight. Thewater pump shaft and seal assembly forms the onlymoving water joint in the cooling system (para 1-13b). Inthe adjustable gland-type pump, normal near of packingwill allow leakage unless gland is tightened periodicallyand packing replaced when worn. Shaft and bearing willbe damaged if packing gland is too tight. In newerpackless-type pumps (para 1-13d), the self-adjusting sealsare subject to wear, deterioration, and leakage. Thrustseal washers and seats are prematurely worn by abrasive

action of sand, dirt, and rust in coolant and by operationwith engine overheating. Bearing and shaft damage,which leads to leakage and pump failure, can result fromneglect of lubrication in pumps that require it. But over-lubrication, especially with a high pressure gun, forcesgrease into the cooling system, which contributes toclogging and overheating.

Figure 2-8. Points of leakage in packless-type pump seal.

Figure 2-9. Leakage in adjustable gland-type pump seal.

c. Effects of Failures and Leakage . Forced coolancirculation is so necessary in the modern cooling systemthat any reduction in pumping capacity causes a loss ofcooling effectiveness. Complete pumping failure is

invariably followed by sudden overheating and operatingdifficulties. Loss of coolant is not the only, trouble that canresult from a water pump leak. Coolant leakage at theshaft, if not properly corrected, will destroy lubrication andcause corrosion and wear of shaft and bearings. Even

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a slight leak at the pump seal or in connections betweenpump and radiator, will allow air to be sucked into thecooling system at high engine speeds (fig. 2-10). Airsuction into the system through a perforated rubber shaftseal can force enough liquid out the overflow pipe to causeserious coolant shortage in a short period of high-speedengine operation. Mixing air with coolant reduces heattransfer and may raise temperature enough to causeoverheating at high engine output. Furthermore,

introduction of air into the system may speed up rusting asmuch as 30 times and also greatly increase corrosion of allcooling system metals (para 2-16c). Clogging andcorrosion go hand-in-hand with neglected waterpumpleakage and air suction.

d. Preventive Service . Since results of pumpingfailure, leakage of coolant, or air suction into the systemcan be serious, water pumps require careful maintenancein the form of frequent inspection, periodic tightening, andproper lubrication. Prompt detection and correction ofleakage is the most important of all water pump preventivemaintenance services.

Figure 2-10. Points of air suction into cooling system.

2-13. Cylinder Head Joint

a. Causes and Effects of Leakage . The joinbetween cylinder head and engine block actually consistsof a large number of individual water joints at watertransfer ports, which are all sealed by one gasket. All othese joints are subjected to the strain of extremetemperature changes within the engine, and also tocombustion pressures as high as 600 pounds per squareinch or more. Internal leakage at the cylinder head gaske

cannot be detected from outside inspection. Leakage ocoolant into the engine (fig. 2-11) can cause seriousdamage, especially in cold weather. Either water oantifreeze solution, when mixed in large quantities withengine oil, will form sludge which may cause lubricationdifficulties. If internal coolant leakage is not promptlydiscovered and corrected, serious engine damage canresult. Even though the joint is tight enough to prevenliquid leakage, the slightest amount of looseness will allowcombustion gases to be blown into the cooling system (fig2-12). This can force coolant out the overflow pipeBurned gases dissolve in coolant to form acids whichcause rapid rust formation and attack metal parts.

Figure 2-11. Coolant leakage into engine.

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Figure 2-12. Exhaust gas leakage into cooling system.

b. Prevention of Leakage . Considering the many

possible points of leakage at the cylinder head joint andthe seriousness of coolant leakage into the engine, it isimperative that the cylinder head always be kept perfectlyleakproof. Cylinder head bolts cannot be evenly tightenedwith an ordinary wrench. Use of a torque-indicatingwrench is necessary to obtain proper uniform pressure onall bolts and to avoid warpage of head or distortion of blockat valve seats and cylinder bores from overtightening. Theextreme importance of maintaining cylinder head jointtightness demands careful attention to all instructions oninstallation of new gaskets, proper order for tighteningbolts, correct torque to apply, and rechecking torquefollowing a new gasket installation. If any stud bolts areloosened in the block when removing cylinder head, they

should be tightened before head is installed.

2-14. Engine Water Jacket

The engine water jacket has many gasketed water jointsand a number of metal water joints in both block and head,where preventive maintenance neglect may result inleakage. Vibration, pressure, and wide changes in enginetemperature, impose strains on all these points. Gasketsdeteriorate from effects of heat, water, and pressure.Gasket joints at thermostat housing and water pumpmounting are common points of leakage. Metal joints,such as core hole plugs, drain plugs, shut-off valves,

temperature gage fittings, and connections at waterbypass or recirculation tubes, are all subject to leakage.Corrosion leakage occasionally develops in metal water

joints. Any leakage at water jacket joints or casting cracksis aggravated by pump pressures which may run as high

as 35 pounds per square inch (fig. 2-2). Pump pressuresare naturally greater at higher engine speeds and while thethermostat is closed. The radiator pressure cap alsoallows additional pressure to build up when the coolant isboiling.

2-15. Accessories Connected to Cooling System

a. Description. Many military vehicles have one omore independent circulating systems connected by hoseor tubing to the engine cooling system for the purpose oheating or cooling of oil coolers, air compressorstransmissions, etc. The water pump circulates coolant toradiators and water jackets of these accessories in thesame manner as to the vehicle radiator and engine water

jacket.

b. Effects of Leakage and Clogging . Leakage inthese units may affect cooling in the entire system eithethrough coolant shortage or by excessive coolancontamination, such as oil from the engine oil cooler. Theunit itself may be damaged by leakage, as in the case ofcoolant leakage into a transmission. Restriction of coolan

flow in the connecting hose and tubes may also seriouslyinterfere with proper operation of such units.

c. Preventive Maintenance . Cooling systempreventive maintenance includes inspection of all speciacirculating systems to see that they are secure, leakproof,and in good condition.

2-16. Cooling System Corrosion

a. Rust Formation . A chemical combination of ironwater, and air produces rust. The water jacket of theautomotive engine has a large mass of iron exposed to the

cooling water, and no cooling system is free of air. Thusall elements of rust formation are found in the coolingsystem. Rust is a product of a chemical process calledcorrosion. Over 90 percent of the solid matter that clogsradiators is rust. Corrosion not only produces harmfuproducts like rust, but also damages iron and other coolingsystem metals. When two different metals, such as ironand copper, are placed in contact with each other and thenimmersed in water, a corrosive action called electrolysistakes place and electric currents flow through the waterfrom one metal to the other in exactly the same mannerthat electricity is produced in a battery. Although thesecurrents are very weak, over a period of time they causelocalized corrosion that weakens, pits, and sometimes

eats completely

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Figure 2-15. Heat cracking at valve seat from rust

clogging.

(2) Radiator clogging. Rust deposits have their mostharmful effects In the radiator. Even a small amount offine rust particles continually circulating through theradiator has a tendency to plate out in he form of a thin,hard scale on the inside of the narrow water tubes (fig. 2-16). This scale first reduces cooling efficiency of theradiator by Insulating tubes from coolant. As more rustbecomes lodged n tubes, circulation is restricted andclogging may progress to the point where coolant will beforced out he overflow pipe. When boiling starts, largeamounts of rust are stirred up in the water Jacket andcarried over into the radiator to completely plug tubes.Further operation of the vehicle will result In seriousoverheating, loss of power, and engine damage.

Figure 2-16. Rust clogging of water passages in tubular radiator core.

d. Corrosion Damage Although a less commoncause of trouble than rust clogging, corrosion damage tometal parts can be equally serious. For example, when awater distribution tube in the block becomes perforated bycorrosion (fig 2-16), coolant distribution in the water jackeis completely upset. Some valve and cylinders will berobbed of proper circulation and cooling, and hot spotsoverheating sticking valves, and even heat-cracking may

follow. Corrosion prevention is especially Important fosuch parts which are so completely hidden within theengine that preventive inspection is Impractical anddetection of failure is difficult. Among other metal partssometimes damaged by corrosion are radiators, watepumps, cylinder heads (figs 2-17, 2-18) and core holeplugs. Thin metal parts are weakened by corrosion andcrack more easily when subjected to vibration and strain.

Figure 2-17. Corroded water distributor tube showing irregular corrosion holes.

Figure 2-18. Aluminum cylinder head showing corrosion damage.

e. Importance of Rust Prevention . A rusty coolingsystem may seem to function satisfactorily undermoderate operating conditions, but will fall to cool theengine under more severe conditions, often at the timewhen full power output is most urgently needed. Thesystem can be kept practically rust-free, and loss ocooling efficiency from rust formation can be avoided byperiodic corrosion-prevention services.

2-17. Prevention of Rust and Corrosion

a. Inhibitors. Protection of the cooling systemagainst rust and corrosion is accomplished by adding

inhibitor to the coolant (para 2-32). Laboratory tests showthat a corrosion inhibitor in water reduces the normarusting of iron at least 95 percent.

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b. Inhibitor in Antifreeze Since inhibitors areincluded in antifreeze compounds (para 2-32c), noinhibitors of any kind should be added to fresh antifreezesolutions. However, corrosion inhibitors may be weakenedby use in the cooling system. Therefore, it is important toadd an inhibitor to reclaimed antifreeze solutions that areto be used a second winter (para 2-32g).

CAUTION

Do not add any more or any less Inhibitor thanspecified in current directives.

c. Inhibitor for Water. Corrosion protection isparticularly important during warm-weather driving whenwater is used as coolant, since there is more air in thecoolant and more rusting in the system. In very coldweather, control of coolant circulation by the thermostatmay reduce flow into the radiator to only a few gallons perminute and very little air is driven into the coolant. In hotweather, with thermostat wide open, the flow Into theradiator at high engine speeds may increase to 100

gallons a minute or more in some engines. The resultingincrease in coolant aeration, together with a higher metaland coolant temperature, greatly speeds up the rate ofrusting (para 2-16b). Installation of inhibitor with watercoolant is a most essential preventive maintenanceservice.

d. Rust Prevention vs Cleaning or Replacement.The time and effort required for adding Inhibitor to a fillingof fresh water or for adding reinhibitor to reclaimedantifreeze solution is only a fraction of what is necessaryfor cleaning a rusty system in which corrosion-preventionservices have been neglected, or for replacing a clogged

or corroded radiator. However, if restriction of flow ofinhibitor is suspected, then flo-tester (3, fig. 2-1) should beutilized to determine amount of restriction.

2-18. Coolant Operating Temperature

a. General. Frequent observation of the enginetemperature gage during operation is a primary preventivemaintenance service for detecting overheating orovercooling of the engine in the first stages, before serioustrouble develops.

b. Overheating difficulties. Excessively high enginetemperatures not only cause "knock" and loss of power,

but also will result in damage to bearings and other movingparts. Cylinder heads and engine blocks are often warpedand cracked by terrific strains set up in the overheatedmetal, especially when coolant is added immediatelyafterward without allowing the engine to cool. Overheatingfirst causes coolant boiling. If the vehicle is operated withboiling coolant, steam pressure forces large quantities ofcoolant out of the system through the radiator overflowpipe. More violent boiling then occurs, and still more

coolant is lost. Finally, coolant circulation stops, andcooling falls completely This means that operating anengine with the coolant boiling for even a short length oftime may be actually driving that engine to destruction.

c. Overcooling Difficulties. Although less sudden ineffect than overheating, overcooling may be equallydangerous to the engine. Low engine operatingtemperature, especially during freezing weather, results in

excessive fuel consumption, dilution of engine oil byunburned fuel, and formation of sludge from condensationof water in cylinders and crankcase. Lubrication failuremay follow sludge formation and lead to serious enginedamage. Burned fuel vapors also mix with water in thecrank case and form corrosive acids which attack engineparts.

d. Temperature Gage Observation (1) To avoid overheating difficulties, the operato

must be constantly alert to see that the temperature gagedoes not exceed the maximum safe operating temperaturespecified for the vehicle. Whenever the gage registers

above this temperature, the vehicle should be halted, theengine stopped, and the cause investigated and correctedbefore further operation is attempted. It is also importanto watch the gage for a sudden rise in temperature duringengine warm-up as an indication of defective cooling.

(2) To prevent overcooling difficulties, keep anynecessary warm-up period before operation as short aspossible, and avoid continued operation of the vehicle ifthe temperature gage does not reach the minimumoperating temperature specified for the vehicle.

(3) When checking for either overheating oovercooling, the possibility of a false temperatureindication from a defective gage should not be overlooked.

(4) Prevention of both overheating and over coolingdifficulties thus requires temperature gage observationsboth before and during operation. It also requires apositive knowledge by the driver or engine operator, of thehighest and lowest safe operating temperature specifiedfor the particular engine.

2-19. Coolant Examination

Another most important cooling system preventivemaintenance service is examination of the coolant fo

color and cleanliness, at least weekly. This can beconveniently done during coolant level inspection bydrawing a sample into a suitable hydrometer or antifreezetester In a system that was reasonably clean when thecoolant was originally installed, the appearance of rust inthe radiator or in the coolant.

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is an indication that the corrosion inhibitor has lost itseffectiveness. Rusty cooling water or antifreeze solutionshould be drained, discarded, and replaced at the firstopportunity. Rust in the radiator, rusty coolant, or coolantcontaining oil or other foreign matter also indicates theneed for preventive cleaning of the system.

2-20. Coolant Level

a. Coolant Level Checking. The level of coolant inthe radiator is the starting point for proper cooling systempreventive maintenance. Coolant level should be checkedaccurately as well as frequently for three separatepurposes: (1) to make sure the system always containsenough coolant, (2) as a guide to cooling system condition;and (3) to avoid overfilling.

b. Coolant Shortage . It is important to make surethat the system contains a sufficient quantity of coolant atall times, if the most common cause of overheating is tobe avoided. Low coolant level may prevent propercirculation, especially at lower engine speeds. At higher

engine speeds, low coolant level allows a large volume ofair to become mixed with the liquid. Air bubbles in thecoolant not only reduce the capacity of the coolant to carryaway heat, but also promote rapid rust formation andcorrosion, and may cause excessive foaming and coolantloss out the overflow pipe. In any case, coolant shortageleads to overheating, operating difficulties, and enginedamage (para 2-18b). Having sufficient cool ant in thesystem at all times is especially important in militaryoperations, due to the necessity of being constantlyprepared for all possible operating emergencies.

c. Coolant Level as Indicator of Cooling System

Condition. The second reason for checking coolant levelis less generally understood. In the military vehicle coolingsystem equipped with a radiator pressure cap, very littlecoolant should be lost through evaporation or from anyother cause if the system is clean, leakproof, and in properworking order. Therefore, any unusual coolant loss over aperiod of normal operation may indicate an impropercondition within the system, any such condition should belocated and corrected before it causes serious trouble.

d. Standard Coolant Level Maintenance Theoperator can assist greatly in the early detection ofirregular conditions inside the cooling system by keepingtrack of the quantities of coolant necessary to maintain the

standard height of liquid level in the radiator as specifiedfor his equipment. The coolant level should always bechecked at approximately the minimum safe operatingtemperature, if possible, since the level rises as the enginewarms up and falls as the engine cools down (para 2-27).

Any unusual increase in the amount of coolant needed tobring the level up to standard height should beinvestigated It should be corrected by the operator orreported by him as a possible indication of troubledeveloping in the system.

e. Overfilling (fig 2-19) If the radiator is continuallyfilled above specified level or when the engine is not up tominimum safe operating temperature, any changes in the

level or the quantity of coolant additions will be of littlevalue as an indicator of cooling system condition. Bothwater and antifreeze expand when heated (para 2-27), andif there is not enough air space left in the radiator for thisexpansion, some coolant will be lost through overflowOverfilling the radiator while using water results in dilutionand weakening of corrosion inhibitor solution (para 2-32)Unnecessary additions of water increase water scaledeposits which interfere with removal of heat from theengine. Overfilling also wastes antifreeze and when asystem containing antifreeze is overfilled with water, it maylead to a freeze-up.

Figure 2-19. Loss of coolant through expansion by heat when radiator is overfilled.

f. Operator’s Responsibility. Coolant levepreventive maintenance services by the operator consisnot only of keeping sufficient coolant in the system at altimes without overfilling, but also include maintaining astandard level at a specified temperature to provide asensitive indication of any hidden trouble that mighdevelop in the system.

2-21. Preventive Cleaning

a. General The cooling system should always becleaned following the draining of rusty or contaminated

coolant before fresh coolant is installed. Neglect ocleaning at this time may result In overheat-

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ing difficulties later. Prompt attention to preventivecleaning is the only sure way to avoid loss of equipmentuse and extra work, time, tools, and materials required forcorrective cleaning of a rust-clogged system. Effectiveand safe preventive cleaning requires that only approvedcleaning compounds be used, and that all serviceoperation specified in current directives be performed.

b. Cleaning Compound. The prescribed cleaning

compound consists of the cleaner and neutralizercompounds packed in separate containers within a singlepackage (para 2-22 (7)).

WARNINGDo not under any circumstances mix cleaningcompound with antifreeze compound or corrosioninhibitor compound. Never mix the water andcleaning compound before putting it into thecooling system. Do not spill compound on skin,clothing, or painted portions of vehicle. If spilled,flush with clean water immediately.

c. Engine Temperature During engine idling periodsrequired in cooling system cleaning processes, it isimportant to cover the radiator and keep the cover

adjusted so that a temperature of 180° to 200°F is

maintained. The engine develops so little heat whilerunning without load that the thermostat valve remainspartially or fully closed. Covering the radiator opens thevalve quickly, but if the cover is removed, the valve willclose again, even though the temperature gage showslittle change. With flow to the radiator restricted by thethermostat valve, cleaning, inhibiting, and flushing are noteffective.

WARNINGRemove radiator cap(s) slowly to relieve pressureand avoid injury to personnel.

d. Cleaning .(1) Drain system by opening drain cocks. Make

certain temperature of coolant has dropped considerably

below 200° F before draining and refilling with cold water

to avoid cracking block and head.

NOTECheck with the cooling system drain caution plateon the instrument panel for position of drains, if the

vehicle is equipped with such a plate.(2) If necessary, use a wire to keep open any drainhole which tends to become clogged.

(3) Disconnect the radiator overflow return-tank, ifthe vehicle is so equipped.

(4) Close the drain cocks, pour water slowly into theradiator until the level is within two inches of overflow pipe.

(5) Replace radiator cap, cover radiator if necessary,start the engine, and run it at idling speed until

temperature reaches above 180° F but not above 200° F.

Then add cleaning components together into hot radiator

in amounts specified on cleaning compound containerAllow engine to continue running for 30 to 60 minutes.

(6) Stop engine and turn radiator cap to releasepressure. As temperature rise can be expected at shutdown, coolant temperature should be allowed to drop

considerably below 200° F before draining and refilling with

cold water to avoid cracking block and head, then removethe radiator cap and drain the system completely.

CAUTIONDo not hold air or water hose too close to radiator,or use excessive pressure as damage to theradiator core may result.

e. Normal Flushing (1) With engine stopped and temperature of coolan

considerably below 200°F, open all drain cocks and

remove engine block drain.

(2) Add clean water and, while so doing, start theengine at fast idle (drains open) Flush, continually flooding

cooling system with clean water, engine running for 25minutes.

(3) Stop engine, close all pet cocks, install engineblock drain, refill with clean water, maintaining level incooling system.

NOTEIf antifreeze compound is to be added afterflushing the radiator, do not add Inhibitor, discardit.

f. Inhibiting. Add inhibitor in amounts specified on

cleaning compound containers to filled radiator, start andrun engine at idle until temperature reaches over 180°F

but not above 200°F.

g. Pressure Flushing (1) To flush radiator (fig 2-20), proceed as follows:(a) Remove both upper and lower hoses connecting

the radiator to engine block.(b) Clamp convenient length hose to radiator core

outlet opening and attach another suitable length of hoseto radiator inlet opening to carry away flushing stream.

(c) Connect the flushing gun to compressed air andto water line and clamp the nozzle of gun in the hose

attached to the radiator outlet opening (lower).(d) With radiator cap on tight, fill core with wateTurn on compressed air in short blasts to prevent coredamage.

(e) Allow radiator to fill with water and again apply aipressure as before. Repeat this process until the watecomes out clear and then proceed as in f above.

(f) Blow insects and dirt from radiator core aipassages, using water to soften obstructions.

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tive.) Maintaining coolant level at all times cannot be overemphasized.

WARNING

Remove radiator cap(s) slowly to relieve pressureand avoid injury to personnel.

b . During initial radiator fill, or refill after coolingsystem has been disturbed in any way to affect coolantlevel, it is important that coolant be added slowly,particularly the last few quarts. This is necessary to permittrapped air to escape and assure that maximum amount ofcoolant has been added to the system. The radiatorshould be filled to the top of filler neck When filling orrefilling cooling system remove the radiator cap (if systemhas two caps both must be removed) and proceed asfollows:

(1) Add coolant slowly until radiator is completelyfilled (never add cold coolant to a hot engine). Excesscoolant, if any, will be automatically expelled through thepressure relief Replace cap(s).

(2) Run engine for about 5 minutes, or if possibleuntil normal operating temperature is reached.

(3) Stop engine and recheck coolant level. Addcoolant as required to bring level to top of filler neck andreinstall cap(s).

c. Defective or improper radiator caps (or pressurerelief valve when applicable) can cause a loss of pressureor abnormally high pressure. Each cooling system isdesigned so that the engine will operate at a temperaturethat is expected to give the best performance PSI (poundsper square inch) rating of the cap (or relief valve)determines the temperature at which coolant will boll. Ifcap or relief valve has a lower PSI rating (defective or

improper) than system requires, coolant will boil at a lowertemperature causing loss of coolant, which if notcorrected, will result in overheating If cap (or relief valve)has a rating too high, the boiling point is raised and morepressure is imposed on the cooling system than it wasdesigned for. This may cause leaks in hoses, connectionsor radiators. The following points pertinent to radiatorcaps are provided for consideration.

(1) During normal operation, if coolant tends to stay

above 200°F, radiator cap may be faulty.

(2) If pressure relief continues to expel coolant belownormal operating temperature level, radiator cap may befaulty.

(3) On vehicles having radiator caps exposed and

subject to damage by crew members stepping on them itis recommended that a "NO STEP" caution be stenciledon the deck near the radiator cap location.

(4) Pressure rating of the radiator cap is stamped ontop surface of cap Assure that cap is the one prescribedby applicable technical manual.

d. Problems with engine cooling fans, drive belts (odrive shafts if applicable) and pulleys have contributed tooverheating problems. Inspection and maintenance othese items should include the following:

(1) Some early 6V53T engines and M551 ARAAVcooling fans were equipped with aluminum pulleys. Earlyfailures resulted in a change to cast iron pulleys. Only casiron pulleys are authorized for use on all cooling systemsfor 6V53, 6V5,3T and 8V71T engines.

(2) Be sure pulleys are tight and properly alinedBurrs, nicks and other sharp edges can cause early beltfailure and should be removed or pulleys replaced.

(3) Fan shafts should be examined for spline obearing wear.

(4) Belts must be properly adjusted for effectiveoperation. Belts that are too loose will slip and beltsadjusted too tight will wear prematurely as well as imposeundue strain on bearings, shafts and pulleys.

NOTEWhere belts are installed in multiples (two or more)they must be replaced in sets because they are

matched sets. Replacing one belt in a set willresult in belt failure since the tighter new belt willbe doing all the work. Refer to the applicabletechnical manual for correct tension andadjustment procedure.

(5) Cooling fan blades must be free of bends, nicksor breaks These fans are precision balanced at time ofmanufacture This balance can be affected by tears, bendsand/or missing chunks which lead to early failure, possibledamage to surrounding parts and injury to personnel.

(6) Observe fans, shafts, pulleys and belts inoperation to be sure all items function properly.

e. Properly functioning thermostats are essential toefficient operation of cooling systems. Defectivethermostats should be replaced but under nocircumstances should engines be operating withouthermostats. Assure that correct thermostat is installed Inthe proper place.

f. Clogged radiator cores restrict engine coolingEvery effort should be made to keep radiators as clean aspossible In some areas dust having a high clay contentends to adhere to the radiator core, frequent cleaning isessential to preclude overheating. Radiator maintenanceshould include.

(1) Remove dirt and other foreign matter fromradiator air passages. Use compressed air or stream o

water to dislodge imbedded material, do not use steamWhen practical, direct air or water from direction oppositenormal intake flow. A radiator and oil cooler cleaning toois available for effective cleaning(10, fig 2-1).

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CAUTION

Do not hold air or water hose too close to theradiator or use excessive pressure as damage tothe radiator core may result.

(2) Radiator core cooling fins that have become bentshould be carefully straightened to assure air passagewithout restriction.

(3) Overflow tube, when so equipped, should becleared using a soft wire probe.

(4) Air intake grille and deck screens must be keptfree of debris, boxes or baggage that may limit the flow ofair. Extra items carried should be stowed withoutinterference to air intake otherwise overheating may result.

(5) Oil spillage on radiator core will tend to hold dust

and block the flow of air Use care to avoid oil spillage onradiator Use cleaning solvent to remove oil spillage.

g. Coolant in radiator, cylinder block, cylindeheads, oil coolers, coolant tubes and hoses must flowfreely without restriction by rust, scale or other sedimentThe cooling system should be cleaned and flushed whennecessary using compound 6850-598-7328. Thiscompound will be used only as necessary and not as aroutine maintenance procedure TB 750-651 establishes

instructions for use.h. Shrouds and panels must be in place to assure

proper air flow and efficient cooling. Engine compartmenpanels, shroud seals, or hull inspection plates will whenremoved change the direction of air flow and adverselyaffect the cooling system.

Section III. TROUBLESHOOTING

2-23. General

This section contains a troubleshooting chart (Chart 2-2)

and information for locating and correcting some troubleswhich may develop in the radiator. Each symptom oftrouble given is followed by a list of probable causes of thetrouble and suggested procedures to be followed toremedy the malfunction.

2-24. Procedures

a . If a specific trouble, test, and remedy are notcovered herein, proceed to isolate the system in which the

trouble occurs and then locate the defect. Do not neglecuse of any test instruments such as thermostat testercooling system tester, flo tester, combustion tester, and

test bench that are available. Standard automotivetheories and principles of operation apply introubleshooting the radiator. Question vehicle operator toobtain maximum number of observed symptoms. Thegreater the number of symptoms of troubles that can beevaluated, the easier will be the isolation of the defect..

b. Good operational trouble analysis depends upona sound and systematic investigation to determine theprimary cause of malfunction.

Chart 2-2. Troubleshooting

Malfunction Probable cases Corrective action

1. Overheating a. Clogged coolant passages a Flush or boll radiator (para 3-11)b. Disintegrated radiator hose b. Replace radiator hose (para 1-5)c. Clogged or bent radiator fins c. Spray clean, splice or replace radiator fins

(para 3-33)d. Frozen radiator tubes d. Clean with acid and boil (para 3-11)e. Shortage of coolant e. Check for leaks Tighten clamps Replace

coolant to proper level (para 2-20)f. Defective or missing thermostat f. Replace thermostat (see pertinent

maintenance manual)g. Dirty radiator g. Drain coolant, clean radiator Add fresh

coolant (para 2-20)2. Overcooling a. Faulty thermostat a. Replace thermostat (see pertinent

maintenance manual)

b. Improper coolant b. Test coolant mixture Add or remove mistureto bring coolant to proper level (para 2-10)

c. Extremely cold weather c. Partly cover radiator Close hood louvers3. Loss of or abnormally high a. Defective or improper radiator cap a. Replace radiator cap (para 1-10)radiator pressure.

b. Collapsed or worn radiator hose b. Replace hose (para 1-6)4. Loss of coolant a. Loose radiator hose a. Tighten hose clamps

b. Defective or improper radiator cap b. Replace radiator cap (para 1-10)

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Malfunction Probable causes Corrective action

4. Loss of coolant (continued) c. Rupture of radiator tube c. Repair, splice, or replace radiator tube (s)(para 3-32)

d. Unsoldered joints, cracked or wornspots or fittings

d. Solder (epoxy) aluminum radiators or patchdefective areas (para 3-43)

e. Open drain cock e. Close drain cock5. Corrosion a. Air in coolant a. Keep coolant level above radiator tubes

(para 2-20)b. Impurities In coolant b. Change coolant frequently (para 2-19)

c. Contamination of coolant c. Drain and clean radiator Add fresh coolant.Check coolant frequently for cleanliness(para 2-19)

6. Foaming of coolant a. Combustion gas leakage into thecoolant

a. Drain coolant Add water then run engine. Iffoaming continues, conduct combustion gas(para 3-21) and air suction test (para 3-19).

b. Air suction into the cooling system b. See a above

Section IV. COOLANT

2-25. Importance of Radiator Coolant

Line an endless belt conveyor, the flow of coolant is

continually carrying a load of heat from the enginewaterjacket into the radiator During operation, transfer ofwaste heat from inside engine to outside air throughcoolant must never be interrupted. Coolant plays asimportant a part in the operation of the automotive engineas fuel or lubricating oil.

2-26. Water as a Coolant

Water has always been the most commonly used coolantfor internal combustion engines because it has good abilityto transfer heat and can be readily obtained almostanywhere. Some properties of water, such as its boilingpoint and freezing point, limits its usefulness as a coolant.The natural corrosive action of water on metals is definitelyundesirable.

2-27. Thermal Expansion

Antifreeze compound solutions expand slightly more thanwater when heated. When the temperature of a 50

percent antifreeze solution is raised from 40° to 180°F, the

solution expands about 1/7 pint per gallon more than waterunder the same conditions. However, during very coldweather, the range between atmospheric and maximumoperating temperatures is much greater than when wateris used, and thermal expansion of solution is therefore a

more serious matter. For example, the expansion of a 50

percent antifreeze solution when heated from -20° to

180°F is nearly ½ pint per gallon. If a 5-gallon cooling

system containing a 50 percent solution where filled

completely full with the coolant temperature at -20°, abou212 pints of solution would overflow out of the radiator by

the time the coolant temperature had reached 180°F.

2-28. Boiling and Evaporation

a. Nature of Boiling Boiling causes coolant tochange rapidly and violently from a liquid to a gas. Boilingof a liquid is controlled by two conditions, temperature oliquid and pressure upon it. Boiling of water takes place a

212° F under pressure of the atmosphere at sea level

When water boils and changes to a gas called steam, it iscapable of expanding 1,600 times. Therefore, a gallon o

water can make as much as 1,600 gallons of steamHowever, when water boils in the limited space of anengine water jacket, this extreme expansion cannot takeplace. Under this condition, the force of the expansioncreates steam pressure.

b. Effect of Altitude (fig. 2-22). Air pressure oneach at sea level is about 15 pounds per square inchThis pressure becomes less at higher altitudes, and thereduced pressure causes water and other liquids to boil aa lower temperature. For example, the reduced aipressure at 1,000 feet above sea level lowers the boiling

point of water from 212° to 210°F. At an altitude of 5,000

feet, the boiling point of water is only 203° F.

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Figure 2-22. Effect of altitude on boiling points of water and antifreeze compound solutions.

c. Effect of Pressure in the Cooling Syste m (fig 2-23). If the pressure in the coolant is raised aboveatmospheric pressure, the coolant will not boll until ahigher temperature is reached. For each pound of

additional pressure in the system, boiling point of the

coolant will rise about 30°F In the military vehicle cooling

system, pressure is applied to the coolant through use of aradiator pressure cap (para 1-10 and 2-9).

2-21

Documents

TM 750-254 Cooling Systems Tactical Vehicles 1972