3387156_coolingsystem

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FOREWARD

A good cooling system troubleshooting procedure

depends upon your knowledge of the cooling system.

This program is designed to give you, the technician, an

understanding of how the components that make up the

cooling system function. Understanding how the proper

operating temperature is maintained, throughout the

engine, should help you become a successful cooling

system troubleshooter.

Use this program in conjunction with Cooling Systems

-Troubleshooting-Program Two, Bulletin No.3387030.

Copyright @ 1980

Cummins Engine Company, Inc.



1. Cooling Systems.

2. The purpose of this program is to familiarize you withthe theory, operation, and components of the

deaerating cooling systems used with Cummins, Engines today.

3. The cooling system performs four basic functions inan engine: absorption, circulation, control, and dis-

sipation.

4. Heat is absorbed from around the cylinder liners and

cylinder heads as the water pump circOlates thecoolant throughout the cooling system.



5. To keep the coolant temperature within the properoperating range, the cooling system must continu-ously dissipate heat from an operating engine.

6. A radiator is normally used to provide a method o

removing heat from the engine coolant and trans-

ferring it to the atmosp~ere.

7. The modern cooling system consists of a number of

components, each matched to the cooling system

requirement.

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{~. Now we'll discuss each part of the cooling system,

-beginning with the water pump. Although built in

several different configurations, the water pump is

basically a housing containing a shaft and impeller

assembly.



9. As the impeller rotates, a low pressure area is formedat its center. Coolant is drawn into this low pressurearea, whirled to the outside by centrifugal force, and

forced out into the coolant passages.

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10. Lubricating oil coolers are also designed in differentshapes and sizes; however, they all perform the samebasic function-using engine coolant to help maintainthe proper lubricating oil temperature.

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11. In this type of oil cooler, the coolant flows through thetubes while lubricating oil flows around the outside ofthe tubes.

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12. In the K series engine oil coolers, the coolant flows

around the outside of the element, while lubricating oilf'ows through the element.



13. Higher horsepower turbocharged engines require anaftercooler, which is basically a heat exchanger in theintake manifold airstream, to either heat or cool the aircoming from the turbocharger compressor. Duringcold weather operations the aftercooler heats theintake air during engine warm-up, while the coolantflow is by-passing the radiator.

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14. During normal engine operation, coolant flows insidethe aftercooler core. At the same time, turbochargedintake air is passing around and through the after-cooler core fins. After being compressed by theturbocharger, this air is usually warmer than theengine coolant. The coolant absorbs a portion of theheat from the intake air, and carries it back to theengine to be dissipated by the cooling system.

15. The thermostat, with the heat sensor protrudIngtoward the engine side of the thermostat housing, islocated in the main coolant stream at the engine wateroutlet connection.

~6. The heat sensor is apressure-tight capsule containing

.J a thermal expansion material. As the engine coolantheats the sensor, this material expands and graduallymoves the shaft, causing the thermostat body to openand allow coolant to flow to the radiator.



17. Until 1975 new engines were equipped with either.vented or non-vented thermostats. The vented

thermostat, which contains a "V" notch or bleed hole,is to be used with non deaerating type systems only.The small amount of coolant by-passed by thisthermostat increases the time required for enginewarm up and can cause cold engine operation inapplications with shutterless systems and low load

factors.

18. The non-vented thermostat is now being used in allCummins engines. The deaerating system purges airfrom the cooling system, both during fill and duringoperation, via a vent line running from the engine sideof the thermostat to the radiator top tank, heatexchanger, or expansion tank. When closed, the non-vented thermostat prevents coolant flow through the

radiator core.

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19. The thermostat seal prevents coolant leakage past thethermostat to the radiator when the thermostat isclosed. Coolant is circulated through the thermostat tothe by-pass system until the thermostat opening

temperature is reached.

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r-20} Radiators are built in two basic styles: vertical and

c cross flow. There is no difference in their basicfunction. The cross flow or horizontal-type radiator wasdesigned for low-profile installations.

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21. In the vertical-type radiator the top tank consists of:, .A sealed baffle plate containing a coolant inlet

connection to the radiator core.

.A fill line tonnecting the top tank to the water pump

inlet.

.An engine vent line connection.

.A baffle vent tube connecting the radiator core to the

top tank cavity.

.And a fill neck with an overflow line.

22. The area between the top of the top tank and the baffleplate is the reserve volume area. This spac-e-serves as areservoir for make-up coolant, in tHe elent coolant islost from the system, -and arso provides space forthermal expansion.

23. An auxiliary tank (or surge tank) is sometimes used on

./ installations that do not have an jntegral deaeratingsystem, or on some applications with "fill" problemsdue to the radiator being lower than the engine, or

other space limitations. The auxiliary tank performsthe same function as the .'reserve volume" area in theradiator top tank.

24. The cooling system should be filled at a minimum rate

--of five gallons per minute. During this time the coolantflows through the fill line, filling both the radiator andengine from the bottom up. The coolant flow forces airto escape through the engine vent line and radiatorcore baffle vent tube into the expansion area in theradiator top tank.



25. The bottom of the radiator fill neck dictates the coolantlevel. When the coolant level reaches this point, a smallamount of air pressure escapes through a bleed hole inthe filler neck, barely allowing coolant to be added intothe expansion area. At the five gallon per minuteminimum fill rate, this will cause the coolant tooverflow the top tank and leave the expansion areavoid of coolant.

26. During initial engine operation, the thermostat isclosed and the water pump circulates coolant throughthe engine, then back to the water pump via the by-pass tube. At this time coolant is also circulatedthrough the engine vent line to the area above thebaffle in the radiator top tank, and returns to the waterpump inlet via the fill line.

27. When the engine coolant reaches thermostat openingtemperature, most of it is routed to the radiator core,below the top-tank baffle plate. Circulating through thecore, the coolant returns to the water pump inlet. While

the thermostat is open, coolant is also circulated to thearea above the baffle plate by both the engine vent lineand radiator core baffle vent tube. This fiow.deaeratesthe system whenever the engine is running.

28. As the temperature increases, the coolant expands,rising past the bottom of the fill neck. The bleed hole inthe fill neck allows the gradual build-up of air pressureto escape into the pressure cap area.



29. The main purpose of the 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 into the system,but reduces the volume of air that is in the system, andraises the boiling point of the cootant.

30. Tests have shown that each psi of pressure in a coolingsystem will raise the boiling point of the coolant byapproximately 3°F. This is especially important ataltitudes where the boiling point is much lower, dus",jtodecreased atmospheric pressure.

31. A pressure cap has two valves-a pressure valve and a

vacuum valve. ~s the coolant expands and pressurebuilds through the fill neck bleed hole, the pressurevalve regulates the maximum pressure by allowing theexcess pressure to escape into the atmosphere.

32. The vacuum valve is a "relief valve" that prevents a

vacuum in the cooling system when the engine beginsto cool after being shut down. At this time it opens,allowing outside air to re-enter the expansion area,thereby equalizing the pressure between the coolingsystem and the atmosphere. In this way the valvesassure close regulation of the system pressure duringthe heating and cooling periods.



33. If the cooling system is not functioning properly andyou suspect a defective pressure cap, check it with apressure cap tester. If the cap does not releasepressure above the psi setting shown on the cap andmaintain pressure at the psi rating, it should be

replaced.

'3j TIJ.e cross flow or horizontal radiator, as we mentioned," earlier, performs the same function as the vertical type

\ in a standard positive-flow system. As the system is--being filled, coolant flows through a fill line, filling both

the engine and radiator from the bottom up. Thisaction vents air from the engine and radiator corethrough the venturi and "U" tube, and the core vent

line, to the "reserve volume" area.

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i35~ During normal engine operation, with the thermostat~ open, coolant enters this radiator at the upper left, and

exits at the lower right. Any entrapped air continues tobe vented to the reserve volume area. When drainingthe cross flow system, the drain valve at the bottom ofthe radiator must be open to drain coolant from the "U"tube. Coolant in the "U" tube will cause an air lock and

prevent the system from filling completely.

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~ In some installations it is necessary to use a heat

ex<.-:hanger n place of a radiator. This is especially truefor marine applications, where sea water is used toabsorb and dissipate engine coolant heat. In theseapplications a sea-water pump circulates sea waterthrough the heat exchanger tubes, then back to the

sea.

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37. At the same time, engine coolant is flowing from theengine, around the outside of these tubes, then backinto the engine. In this way outside water carries awaythe heat from the engine coolant

38. Engine coolant is vented to the expansion space in theheat exchanger housing to allow deaeration during filland engine operation.

39. In marine applications using keel-coolers, the heatexchanger function takes place as the engine coolantis circulated through the keel cooler. With the heatexchanger core removed, the housing now becomes

all expansion space. In either system, an auxiliary tankmay be added to provide reserve coolant and

expansion capacity. Notice the coolant flow in themarine gear oil cooler (left bank). Coolant flowsthrough the element tubes, while the gear oil flowsaround the outside of the tubes.

40. Cooling system hose must be relatively flexible, yetrigid enough so it will not collapse. It should havesmooth inner walls. Using molded hose with coil-wirereinforcement, or highly-flexible "accordion" hosereduces the effective inside diameter of the hose, andmay cause aeration and a significant pressure drop inthe system.



41. Another part closely associated with the radiator is theradiator shutter assembly. Shutters are used as asupplement to the engine thermostat to assist inmaintaining the engine at the proper temperatureduring operation. The shutter assembly accomplishesthis by regulating the air flow across the radiator coreand through the engine compartment.

42. The shutterstat control is a heat-sensitive device whichuses the force of air pressure, vacuum, engine lube oil,or electric power to open and close the shutters.Manual controls are also available. The shutterstatcontrol is usually installed in the coolant flow in the

thermostat housing.

43. The cooling fan plays an important role in the coolingsystem. The main function of the fan is to pull or pushair through the radiator core. This air carries awaycoolant heat as it passes through the core tubes and

fins.

44. Equally important are the fan drives. The temperature-

sensing or "thermatic" fan drives provide noisereduction and a savings in horse-power (fuel savings)when not in operation. The fan drives used on the K-6and VTB-903 series engines are the thermo-modulating type fan drives. These are spring loaded,oil cooled, multi plate clutch drives designed to providevarying fan-to-engine speed ratios. The variable slip ofthese drives assures the prescribed engine coolanttemperature with minimum engine horsepower loss.



45. Air pressure for clutch control is provided by a thermalair valve located in the engine thermostat housing.Sensing engine coolant temperature through a thermaltip, the valve regulates air pressure to the clutchaccording to the coolant temperature in the thermostat

housing.

46. This "on-off' type thermatic fan drive is also airoperated. A built-in multiple disc clutch, that is

normally engaged by spring pressure, turns the fanwith the pulley. When cooling is not required air

pressure, regulated by the thermal control valve,automatically disengages the fan.

47. Variable-speed viscous fan drives are air-temperaturecontrolled by means of a leaf-type bi-metal strip thatcan be located on either the front or back side of thefan drive. This device senses air temperature changes

in the air that passes through the radiator core andmoves an internal valve, thereby regulating the flow ofviscous fluid from the reservoir. The amount of fluid inthe drive area controls the fan speed.

48. Thermatic fan and shutterstat controls must be setaccording to the specifications in the appropriateOperation and Maintenance Manual.



49. Fan shrouds are used on many installations to improvecooling efficiency, provide a uniform distribution of airover the core, and to restrict the recirculation of air

around the fan blades. When installed as originalequipment in a cooling system, the fan shroud should

not be removed.

50. Recirculation baffles around the radiator help preventthe recirculation of hot air from the engine compart-ment to the front of the radiator core. If these bafflesare damaged or removed, the engine coolanttemperature may rise much higher than normal.

?f: The inside of the radiator core, as well as the rest of thecooling system, must be free from obstructions.Chemical cleaning and flushing with a neutralizer andclean water will normally remove these contaminantsfrom the system.

52. In extreme cases it may be necessary to remove and

dismantle the radiator to remove the rust, scale, andsolder corrosion that have collected in the radiator

core.



53. The system should also be thoroughly cleaned andflushed when anti-freeze is changed. At anytime thecoolant is changed the system must be pre-chargedwith one unit of DCA for each gallon of cooling system

capacity.

54. To maintain this concentration of DCA chemicalinhibitor and to filter out dirt, rust particles and otherforeign material from the cooling system, the DCAcorrosion resistor must be changed at the propermaintenance intervals.

55. A test kit is available for checking the coolant to insureproper DCA unit concentration. This kit tests for thenitrite level of the coolant, which is the chemical

.responsible for preventing cylinder liner corrosion.

56. Drive belts also play an important role in the cooling

system. Although gear-driven water pumps and fanhubs are now being used on some Cummins engines,most production engines are currently using Poly-Vbelts to drive the water pump.



57. When replacing belts always shorten the distance

between pulley centers. Rolling a belt over a pulley, or

using a screwdriver, will damage the belt and cause an

early failure.

58. Always replace matched belts as a complete set of thesame manufacture and same length. These belts willassume equal loads, and will stretch at the same rate,giving maximum service.

59. Always keep the belts tightened to the proper tension.Follow the instructions and specifications in theappropriate Operation and Maintenance Manual.

60. Now that we've discussed the cooling system com-

ponents and their function, let's take a look at thecoolant flow through the NT engine.



61. The Big Cam II is the FFC (Full Flow Cooling) enginethat now has the DFC (Demand Flow and Cooling)lube oil system. However, this new lube oil systemdoes not change the coolant flow.

62. In the FFC engine the coolant flows from the water

pump to the water header plate. At this pointapproximately Y3 of the coolant is diverted from thecylinder block and is routed through the oil cooler andwater transfer tube to the thermostat housing.

63. The remaining coolant circulates through the engineand back to the thermostat housing. When thethermostat is closed, the coolant flows through thecenter of the thermostat and is channeled through aby-pass tube back to the water pump.

64. When the engine reaches thermostat opening

temperature, the coolant flow is directed to the radiatorcore. After circulating through the radiator core thecoolant flows back to the water pump. A portion of thecoolant is by-passed through the DCA corrosionresistor for treatment during engine operation.



65. Wall charts of engine cutaway artwork are available forall engine series. These charts show internal passages

of the engines and compo.nents.

\/66. This program should prepare you for troubleshootingthe cooling system. Effective, successful trouble-shooting requires a thorough knowledge of the engine

systems, parts and functions.

,/67. And remember, a well designed and properly main--tained cooling system will protect the engine and

allow many miles of cost-efficient operation. y

NT(FFC)EXHAUSr SIDE VIEW



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