3387029coolingsysIntroToTroubleShootPrg1

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FOREWORD

Have you ever seriously thought about thecooling system in a diesel engine? Its purpose,

how it functions, and why?

In this program we've tried to cover these

questions well enough so that you can easily

understand them. We're sure that, when you

thoroughly understand this system, you will

become a highly-successful cooling-system

troubleshooter.



1.

2. The purpose of this program is to familiarize you

with the theory and operation of the cooling

systems in Cummins Engines.

3. You can then apply this knowledge when you see

the second Cooling System Program, which will

deal with troubleshooting and failure analysis.

4. Some people feel that the cooling system consistsof a big radiator, and all you need to do is keep it

filled with water.

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5. Actually, water is a very important part of the

cooling system. So is the radiator or heat

exchanger. But these things make up only a small

portion of a complete system. This fact is easy to

believe if we understand the purpose of a cooling

system.

6. It performs four basic functions in an engine:absorption, circulation, control, and dissipation.

7. The coolant absorbs heat from areas around the

cylinder liners and cylinder heads. ( Remember

that heat flows from warm areas to cooler areas.)

8. The water pump circulates the coolant throughoutthe entire system.

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9. The thermostat, shutters, and the cooling fan

control engine coolant in order to keep it within.

the temperature range required for optimum

;engine operation.

10. A radiator or heat exchanger provides a way for

engine heat. to be removed, or dissipated, from the

engine coolant and transferred to the atmosphere,

or to an outside water source.

~11. Now we'll discuss each part of a modern cooling

system. Let's begin with the centrifugal water

pump. Although it's built in many Qifferent

configu rations,

12. it is basically a housing containing a shaft and

impeller assembly. As the impeller turns, it creates

a pressure differential across the pump.

3



13. This pressure differential forces the coolant to

circulate through the system. The head of pressure

from the volume of coolant above the water pump

maintains a constant pressure at the water pump

inlet. This area must always be under a positive

pressure to aid in keeping air out of the system.

1~ Oil coolers are made in different.shapes .and sizes,

: ! but they all perform the same basic function.II

15. Coolant flows through the tubes In th is type of

cooler, while the oil flows around the outside ofthese tubes.

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16. In the K series coolers, the coolant flows around

the outside of the element, wh ile the oil flows

through the element.

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17. So, during engine operation, the coolant helps

maintain a satisfactory lube oil temperature range.

18. As the coolant passes through the block and head

passages, it absorbs heat from the cylinder liners,

and the injector and valve areas.

19. Higher horsepower turbocharged engines use an

aftercooler to cool the air coming from the turbo.

20. During normal ehgine operation, coolant flows

through the core tubes. At the same time, intake

air is passing from the turbo around theaftercooler core tubes. After being compressed,

this air is usually much hotter than engine coolant.

So the coolant absorbs a portion of the heat from

the intake air, and carries it through the the

.radiator or heat exchanger ..

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21. The thermostat is located in the main coolant

stream, near the upper, front part of the engine,

just before the radiator or heat exchanger.

22. The heat sensor protrudes toward the engine side

of the thermostat housing.

23. It is basically a sturdy, pfessure-tight capsule

containing a thermal expansion material, usually a

composite of wax and copper powder. As the

engine coolant heats the sensor, the wax melts and

expands, gradually moving a stainless-steel shaft a

predetermined distance. This movement causes the

thermostat body to open, allowing coolant to flow

to the radiator .

24. Until 1975, new engines were equipped with two

basic types of by-pass thermostat -vented and

non-vented, Now the vented thermostat is no

longer current for service. It contains a "V" notch

which allows a small ~mountof coolant and air to

bypass the valve during fill and during engine

operation. The small amount of by-passed coolant

may cause a lightly-loaded engine to run extremely

cold. A shutterless system tends to intensify t.hi~problem of cold operation. .

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..25. The ventless thermostat is usr..-j In a positive-flow

deaerating system. This system purges air from the

eng,ine during fill and du'ringoperation via a vent

line running from the engine side of the

thermostat housing to the upper part of the

radiator, heat. exchanger or expansion tank. The

ventless thermostat prevents any flow through the

radiator core when the thermostat is closed.

26. The thermostat seal keeps the coolant from

passing on to the radiator when the thermostat isclosed.

27. Radiators are bu ilt in two basic styles: vertical and

cross-flow. There is no difference between their

basic functions. The cross-flow type was designed

for low-profile installations.

28. In the vertical type, the top tank consists of a

sealed baffle plate, a fill line connecting the top

tank to the water pump, a coolant inletconnection, a vent line connecting the radiator

core to the top tank cavity, a vent line inlet from

the engine, and a fill neck with an overflow line.

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29. The area between the top of the top tank and tht:baffle plate is the reserve volume. 1"his space servesas a reservoir to store make-up coolant to be used

when water is lost from evaporation and minor

leaks.

30. It also provides space for thermal expansion.

Through a 40° to 200°F. temperature range,lwater

expands at the r-ate of approximately 1/3 pint for

each gallon in the system.! When 50% anti-freeze is

added, this expansion' increases slightly. If

expansion space is not provided, this amount of

coolant will be lost through the overflow line.

31. The cooling system should be filled at the rate ofapproximately five gallons per minute. During this

time, the co'Qlant flows through the ~i" line, into

the system.

32. At this time, air is escaping through the vent lineand vent tube to the reserve volume in the radiator

top tank.



33. The bottom of the fill neck dictates the coolant

level. When the coolant reaches this point, a small

amount of air pressure escapes through a bleed

hole in the filler neck. But this air escapes so

slowly that it barely allows coolant to be added,

even at a very slow rate.

34. During initial engine operation, the water pump

forces pressurized coolant through engine passages.Since the engine is cold, the thermostat is closed,

and the coolant is routed through the bypass tube,

back into the water pump and engine, and anyaccessories attached to the engine side of the

thermostat.

35. When the engine coolant reaches normal operating

temperatures, the thermostat is open. Most of thecoolant is then routed through the radiator inlet

line to the radiator core, below the top-tank baffle

plate.

36. At this time coolant is expanding, rising past thebottom of the fill neck. The bleed hole allows the

gradual build-up of air pressure to escape directlyto the pressu e cap area.

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37. Without this bleed hole, air pressure would force

the coolant {and any air in the fill neck) out of the

system as it expanded.

38. An auxiliary tank is sometimes used on

installations that do not have an integral

deaerating system, or on installations with "fill"

problems, due to the radiator being lower than the

engine, or space limitations. This tank performs

the same functions as the "reserve volume" area in

a positive-flow system top tank.

39. The standard cross-flow radiator, as we mentioned

earlier, performs the same functions as the vertical

type, in a standard, positive-flow system. As the

system is being filled, coolant flows through the

fill line. In this way, both the radiator and engineare filled from the bottom up. This action vents air

from the engine and radiator core through the

venturi and ',U" tube, and the core vent line, to

the "reserve volume" area.

40. During normal engine operation, with the

thermostat open, coolant enters this radiator atthe upper left, and exits at the lower right. Any

entrapped air continues to be v~ted to the reservevolume area.

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41. In some installations, it is necessary, and usually

convenient, to use a heat exchanger in place of a

radiator. This is especially true for marine

applications, where it is not desirable to blow a

great deal of heat into the cabin area from a

cooling fan. Sea water is used to absorb and

dissipate engine coolant heat.

42. The heat exchanger works exactly like an oil

cooler. A sea-water pump circulates sea water

through the heat exchanger tubes, then back to

the sea.

43. At the same time, engine coolant is flowing from

the engine, around the outside of these tubes, then

back to the engin~. In th is way, outside water

carries away the heat from the engine coolant.

44. Engine coolant is vented to the expansion space in

the heat exchanger housing to allow deaeration

during fill and engine operation.

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45. In keel-cooling applications, the heat exchangerfunction takes place as the engine water Is cooled

by the keel cooler. With the heat exchanger core

removed, the housing now becomes all expansionspace. In either system; an auxiliary tank may be

added to the system to provide reserve coolant and

reserve expansion capacity. Notice the 'coolant

flow in the gear oil cooler (left bank). Coolant

flows through the element tubes, while the gear oil

flows around the outside of the tubes.

46. Many institutio,nal installations use heat

exchangers. Fresh water is piped to the heatexchanger from the city water supply or from

private wells.

.47. The main purpo~ of a radiator pressure cap is to

increase the pressure level of the total system. A

positive pressure (greater than atmospheric

pressure) not only prevents the entry of more air

in the system, but it reduces the volume of air that

is already in the system, and it raises the boiling

point of the water .

48. A pressure cap has two valves -a pressure valve

.and a vacuum valve. As the coolant expands during

engine operation, the pressure valve regulates

maximum pressure by opening and allowing the

escape of excessive pressu re.

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.49. When the engine is shut down and begins to cool,

the pressure valve is closed. The vacuum valve is a

"relief valve" which prevents a vacuum in the

cooling system. It opens at this time and allows

outside air to re-enter the expansion space,

thereby equalizing the pressure between the

system and the atmo~phere. In this way, the valves

assure close regulation of system pressure during

the heating and cooling periods.

\

.50. The pressure cap raises the boiling point of the

coolant. At an atmospheric pressure of 29.92 in.

Hg., water will boil when its temperature reaches

212°F. (100C.).

.51. However, when air pressure in the top tank

exceeds the vapor pressure of the coolant, the

water cannot boil. And it won't boil until the

vapor pressure exceeds the regulating pressure of

the pressure cap valve, and escapes to the

atmosphere.

~

.52. Tests have shown that depending on many

variables, e=3ch additional psi of air pressure willraise the boiling point of the coolant by

approximately 3°F. This is especially important at

altitudes where the boiling point is much lower,

due to low atmospheric pressure.

"

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.53. So what would happen if the pressure valve was

blocked in the closed position? Right! The coolant

pressure would eventually rupture the weakest

area in the system -usually in the radiator core or

a water hose.

.54. And what wou Id happen if the vacuum valve sticksopen? Right again! The system would notpressurize, and boiling would occur at much lower

tern peratu res.

55. If you suspect that the cap is defective, check it

with a pressure pump. Set the pump gauge at the

psi shown on the cap. If the cap does not release

the pressure near this setting, it should be

replaced.

If you suspect that the vacuum valve is defective,

shake the cap. If the vacuum valve is proper1y

seated, it will not rattle.

56. Cooling system hoses must be relatively flexible,

yet rigid enough so they will not collapse. They

should have smooth inner walls. Hoses with

coil-wire reinforcement, or the highly-flexible

"accordion" hoses, will create water turbulence.

This design reduces the effective diameter of the

hose, and causes a significant pressure drop in the

system.

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57. Another part closely associated with the radiator is

the radiator shutter assembly. Shutters are used as

a supplement to the engine thermostat to assist in

maintaining minimum coolant temperatures during

engine operation. They accomplish this by

regulating the air flow across the radiator core and

through the engine compartment.

58. The shutterstat control is a heat-sensitive device

which uses the force of air pressure, vacuum,

engine lube oil, or electric power to open and close

the shutters. Manual controls are also available.

The shutterstat control is usually installed in the

coolant flow in the thermostat housing.

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59. The cooling fan plays an important role in the

cooling system. The main function of a fan is to

pull or push air through the radiator core. This air

carries away the coolant heat as the coolant passes

through the core tubes and fins.

.60. Fans come in a wide variety of blade shapes, pitch,

hub types, diameters, and materials to fit almost

any type of installation.

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61. Equally important are the drives. Very popular

nowadays, because of the horsepower savings and

the no ise reduction, are the

temperature-controlled, or "thermatiG "fan drives.

This "ON-OF F" type of drive is air-operated..

When the air temperature drops to a

pre-determined level, air pressure forces a built-in

clutch to disengage from the fan hub.

62. Variable-speed viscous fan drives are

air-temperature controlled by means of a leaf-type

bi-met~1 located on the front of the fan. This

device senses air ter1'1perature changes in the air

that has passed through the radiator core.

63. The bi-metal moves an internal valve which

regulates the flow of a viscous fluid from a

reservoir. The amount of fluid in the drive area

controls the fan speed.

64. Thermatic fan and shutterstat controls must be setaccording to the specifications in the appropriate

Operation and Maintenance Manuai.

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-65. Fan shrouds are used on many installations to

improve cooling efficiency, provide a uniform

distribution of air over the core, and to restrict the

recirculation of air around the fan blades.

.66. Recirculation baffles around the radiator help

prevent the recirculation of hot air through the

radiator core. If these baffles are damaged or

removed, engine coolant temperatures may rise

much higher than normal.

-67. The inside of the radiator core, as well as the restof the cooling system, must be free from

obstructions.

.68. If rust. and scale have collected in the system, it

must be chemically cleaned, then flushed with agood neutralizer and clean water .

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69. The system should also be thoroughly cleaned and

flushed when anti-freeze is added or removed, or

before installing a water filter on anew engin~.

Nc 2 t

.70. The DCA Water Filter is a definite "must" in a

cooling system. This filter performs four functionsin an engine. .

~ 71. One, it provides a positive method of filtering out

dirt, rust particles, and ot:her foreign material from

the cooling system.

72. Two, it controls the acidity level in the coolant byreleasing special buffering agents in the system.

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.73. Three, it slows down the formation of rust by

adding a corrosion-inhibiting chemical to the

coolant. This chemical prevents corrosion of

cylinder Ijners, solder, aluminum, copper and

brass.

,74. And four, rt slows down the rate of scale build-up

by softening the water .

75. A test kit Is available for checking the coolant to

make sure that filter servicing or concentration of

DCA inhibitor is adequate (but not excessive) to

control corrosion for any specific operatingcondition.

76. For information concerning complete maintenanceprocedures, refer to CST program No.3387001and the appropriate Operation and Maintenance

Manual.

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77. Drive belts playa most important role in a cooling

system. Although K engines have gear-drjven water

pumps, all other current production engines use

drive belts for water pumps and radiator fans.

78. Cummins I engines use either V-belts or Poly-V

belts. V-belts contain either rayon or polyester

cord. Polyester-cord belts are tougher and more

durable than comparably.;sized rayon belts.

79. Poly-V belts are used mainly on K engines. The

term "Poly' as used here, simply means that the

belt contains several "V" channels.

80. Cog-type belts are used with small pulleys. The

spaces between the cogs allow the belt to bend in a

smaller radius with less strain.

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81. When replacing belts, always shorten the distance

between pulley centers. Rolling a belt over a

pulley, or using a screwdriver, will ~amage the belt

and cause an early failure.

82. Always replace belts as a complete new set, of the

same manufacture and the sar'ne length. Thes.e

belts will assume equal loads, and will stretch at

the same rate, giving maximum service.

~3. Let's assume that a new belt is installed with a set

of old belts. The new belt is the same length as the

old ones, but the part number and manufacturer

.are different. Would this arrangement work OK?

Definitely not! The new belt will stretch, while the

old belts remain the same. This throws the full

load on the old belts.

84. Or, let's say that a new belt is installed with an old

set of the same part number and manufacturer.

Now what happens? Still bad news The old

belts are already stretched. So, for awhile, the new

belt carries the full load, and it will probably fail

in a short period of time.

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85. Misalignment of pulley grooves must not exceed

1/16 inch per foot of distance between pulley

centers. Angular misalignment must not exceed

one-third of one degree.

86. Belts must not bottom on pulley groove~, norshould they protrude more than 3/32 inch abovethe top edges of the grooves. Riding depth mustnot vary over 1/16 inch on matched belt sets.

87. Always keep the belts tightened to the proper

tension. Follow the instructions and specifications

in the appropriate Operation and Maintenance

Manual.

88. We've discussed most of the cooling system parts

and their functions. Now we'll take a look at the

coolant flow through some of our engines.

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89. In the earlier 855 Cu. In. engine, coolant flows

from the water pump through the engine. When

the engine is cold, the coolant is bypassed from

the engine side of the thermostat housing to the

oil cooler. It is recirculated through the engine and

any accessories attached to the engine side of the

thermostat. A portion of the coolant flow

bypasses through the water filter during engine

operation. (Remember, a vented thermostat would

allow a small amount of coolant to flow through

the radiator at this time.)

90. When the engine reaches normal operating

temperatures, the thermostat opens. Coolant thenflows through the radiator, oil cooler, and back tothe water pump.

91. On NT A engines, coolant flows from the rear

block water header, through the aftercooler core,then to the thermostat housing. Coolant also flows

through the air compressor.

92. In the FFC engine, coolant flows from the water

pump to the water header plate. At this point,

approximately 1/3 of ttle coolant is divertedthrough the oil cooler and water transfer tube tothe thermostat housing.

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93. The remaining coolant circulates through theengine, and back to the thermostat housing. Whenthe thermostat is closed, coolant flows through theby-pass tube, back to the water pump. (Coolant is

continually by-passed through the water filter

during engine operation.)

94. When the engine reaches normal operattng

temperatures, the thermostat opens. Coolant then

flows through the radiator, directly back to the

water pJmp. Coolant flow in the engine

accessories, such as the water filter, cab' heater, or

air compressor, is similar to that in the NT A

engine.

95. In the KT -6 engine, coolant flows from the water

pump through the oil cooler, then through the

cylinder block, cylinder heads, water manifolding,

and to the thermostat housings. .From here the

coolant flows through the by-pass tube back to thewater pump. Coolant is continuously by-passed

from the pump, through the water filter, and back

to the pump.

96. When the engine reaches normal operating

temperatures, the thermostat opens. Coolant' isthen routed through the radiator, then back to the

water pump,

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97. I n the V -1710 engine, coolant flows from the

water pump, through the oil cooler, rear block Vee

connection, and block Vee water header. From

this point, it flows to the aftercoolers, block liner

cavities, cylinder heads and exhaust manifolds (if

water-cooled). These flow circuits lead to the

thermostat housings. Then, depending on engine

temperatures, .coolant bypasses back to the water

pump or flows to the radiator/heat exchanger.

98. In the V-504 marine engine, coolant flows from

the water pump, around the cylinder liners, to the

cylinder heads and exhaust manifolds, then to the

thermostat housing. At this point, coolant flows

back to the water pump or through the heat

exchanger, depending on engine operating

temperature. Coolant flows continuously, in a

bypass circuit, from the cylinder block to the

engine and gear oil coolers, and back to the block.

99. In the V-903 engine, coolant flows from the waterpump to the oil cooler, right-bank water header

plate, right-bank cylinder Hners, cylinder head, andright-bank thermostat housing. At the same time,

coolant flows from the water pump through thewater crossover to the left-bank water header

plate, cylinder liner.s, head and thermostat

housing. Depending on engine .operatingtemperatures, coolant flows directly back to thewater pump or through the radiator, then back tothe .pump.

100. We've discussed most of the basics involved in

Cummins cooling systems, including coolant,0

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101. cooling system parts,

102. and coolant flow through several engines.

103. As we mentioned earlier, the main purpose of this

program is to prepare you for troubleshooting this

system. Remember, "effective, successfuJ

troubleshooting requires a thorough knowledge ofthe engine systems, parts and functions".

104.



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3387029coolingsysIntroToTroubleShootPrg1