NOTE: The 3100 HEUI Electronic Control System will activate fault codes to warn of engine overheating. Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566, Event Codes Test.
* Low Coolant Level
* Incorrect Mixture
* Air In Cooling System
* Fan Clutch
* Temperature Gauge
* Sending Unit
* Radiator Cap
* Incorrect Fan, Fan Or Shroud Not In Correct Position
* Loose Belt(s)
* Air Inlet Restriction
* Exhaust Restriction
* Shunt Line
* Water Temperature Regulator
* Defective Water Pump
* Air Flow Through Engine Compartment
* Outside Temperature
* Operate At High Altitude
* Engine Used In Lug Condition
1. Low coolant level:
If the coolant level is too low, not enough coolant will go through the engine and radiator. This lack of coolant will not take enough heat from the engine and there will not be enough flow of coolant to release the heat into the cooling air. Low coolant level is caused by leaks or incorrect filling of the radiator. With the engine cool, be sure that coolant can be seen at the low end of the fill neck on the radiator top tank.
2. Incorrect mixture:
Check the mixture of antifreeze and water. The mixture should be approximately 50 percent water and 50 percent antifreeze with a 3 to 6 percent coolant conditioner. If the system is not correct, drain the system as needed and put the correct mixture of water, antifreeze and coolant conditioner in the cooling system.
3. Air in cooling system:
Air can enter the cooling system in different ways. The most common causes are not filling the cooling system correctly, and combustion gas leaking into the cooling system. Combustion gas can get into the system through inside cracks, a defective cylinder head, leaking unit injector sleeve, or head gasket. Air in the cooling system causes a reduction in coolant flow and bubbles in the coolant. Air bubbles hold coolant away from the engine parts, preventing the transfer of heat to the coolant.
4. Fan clutch:
A fan clutch not turning at the correct speed can cause improper air speed across the radiator core. The lack of proper air flow across the core can cause the coolant not to cool to the proper temperature differential.
5. Temperature gauge:
A temperature gauge which does not work correctly will not show the correct temperature. If the temperature gauge shows that the coolant temperature is too hot but other conditions are normal, either install a gauge of known accuracy, or check the cooling system with the 8T0470 Thermistor Thermometer Group. Compare temperature gauge with coolant temperature on the display status screen of the electronic service tool.
6. Sending unit:
In some conditions the temperature sensor in the engine sends signals to a sending unit which converts these signals to an electrical impulse which is used by a mounted gauge. If for some reason the sending unit malfunctions or the electric wire breaks or shorts out the gauge can show an incorrect reading.
a. Restriction to flow of coolant through core tubes of radiator of air flow restriction. Check for debris between the fins of the radiator core which prevents free air flow through the radiator core. Check the radiator for debris, dirt, or deposits on the inside of the radiator core which will prevent free flow of coolant through the radiator.
b. A radiator which is too small does not have enough area to release the heat to the cooling air. This will cause the engine to run at a higher than normal temperature. Make sure the radiator size is according to the OEMs specifications.
8. Radiator cap:
A pressure drop in the radiator can cause the boiling point to lower causing the cooling system to boil over. A cooling system pressure tester may be used to check the cooling system pressure as well as the pressure cap relief valve. If the cap fails the test, check the rubber seal on the cap as well as the operation of the pressure relief valve.
9. Incorrect fan, fan or shroud not in correct position:
A incorrect fan, or a fan or shroud in a wrong position will cause a reduction or a loss of air flow through the radiator. The fan must be large enough to send air through most of the area of the radiator core.
10. Loose belt(s):
Loose fan or water pump belts will cause a reduction in air and coolant flow. Tighten the belts according to the Belt Tension Charts.
Defective hoses with leaks can normally be seen. Hoses that have no visual leaks can collapse (pull together) during operation and cause a restriction in the flow of coolant. Hoses become soft and/or get cracks after a period of time. Hoses must be changed after 3000 hours or two years of use. The inside of a hose can deteriorate, and the loose particles of the hose can cause a restriction of the coolant flow.
12. Air inlet restriction:
Restriction of the air coming into the engine can cause high cylinder temperatures and more than normal amount of heat to pass to the cooling system. Check for restriction with a water manometer or a vacuum gauge (which measures in inches of water). Connect the gauge to the engine air inlet between the air cleaner and the inlet to the turbocharger. With the gauge installed, run the engine at full load rpm and check the restriction. Maximum restriction of the air inlet is 6.22 kPa (25 inches of water). If the indication is higher than maximum permissible restriction, remove the foreign material from the filter element, or install a new filter element and check for the restriction again. If the indication is still too high, there must be a restriction in the inlet piping.
13. Exhaust restriction:
Restriction in the exhaust system can cause high cylinder temperatures and more than normal amount of heat to pass to the cooling system. To check if there is an exhaust restriction, make a visual inspection of the exhaust system. Check for damage to piping or for a defective muffler. If no damage is found, check the exhaust system for back pressure from the exhaust (pressure difference measurement between exhaust outlet and atmosphere). The back pressure must not be more than 10.0 kPa (40 inches of water). Check the system by removing the exhaust pipes from the exhaust manifolds. With the exhaust pipes removed, start and run the engine to see if the problem is corrected.
14. Shunt line:
A restriction of the shunt line from the radiator top tank to the engine water pump inlet, or a shunt line not installed correctly, will cause a reduction in water pump efficiency. The result will be low coolant flow and overheating.
15. Water temperature regulator:
A water temperature regulator that does not open, or only opens part of the way, can cause above normal heating. To test the water temperature regulator, see the Testing and Adjusting Section of the Service Manual.
16. Defective water pump:
A water pump with a loose or damaged impeller does not pump enough coolant for correct engine cooling. Remove the water pump and check for damage to the impeller. If the impeller has no damage, check the impeller clearance.
17. Air flow through engine compartment:
The air flow through the radiator comes out of the engine compartment. Make sure the filters, air conditioners and similar items are not installed in a way which prevents free flow of air into and out of the engine compartment.
Restriction of air flow through the air-to-air aftercooler (if equipped). Check for debris or deposits which would prevent the free flow of air through the aftercooler.
19. Outside temperature:
When outside temperatures are too high for the rating of the cooling system, there is not enough temperature difference between the outside air and coolant temperatures.
20. Operation at high altitude:
The cooling capacity of the cooling system goes down as the engine is operated at higher altitudes. A system, under pressure, large enough to keep the coolant from boiling must be used.
21. Engine used in a lug condition:
“Lugging” Lugging can occur when there is too much load applied to the engine or the engine is run at a lower rpm. This low rpm causes a reduction in air flow through the radiator, and a reduction in the flow of coolant through the system. This combination of less air and less coolant flow during high input of fuel will cause above normal heating.