Probable Causes
- Plugged cooling fins for the radiator
- Problems with the cooling fan
- Extreme operating conditions
- Water temperature regulator
- Faulty radiator cap
- Radiator
- Faulty water pump
- Low coolant level
- Incorrect coolant mixture
- Air in cooling system
- Faulty temperature gauge
- Faulty sending unit
- Worn hoses or damaged hoses
- Air inlet restriction
- Exhaust restriction
- Restriction of the shunt line
- Restricted air flow through the aftercooler
- Incorrect fuel setting
- Incorrect fuel injection timing
Recommended Repairs
Plugged Cooling Fins for the Radiator
Clean obstructions in cooling fins for the radiator.
Problems With the Cooling Fan
Check for proper operation of the cooling fan. Check applicable drive belts, pumps, speed sensors, and/or solenoids for proper operation.
Reduced airflow through the radiator can be caused by one of the following items:
- Incorrect fan
- Improperly positioned fan shroud
- Damaged fan blade
The fan must be large enough to send air through most of the area of the radiator core.
Loose fan drive belts or loose water pump belts will cause a reduction in air and coolant flow. Tighten the belts to the proper tension. Refer to Specifications, "Belt Tension Chart".
Extreme Operating Conditions
Determine if the engine is operating under extreme outside temperatures or high altitudes.
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.
The cooling capacity of the cooling system goes down as the engine is operated at higher altitudes. A pressure type cooling system must be large enough to keep the coolant from boiling.
Running an engine at lower engine speeds can cause the engine to lug. This low rpm causes a reduction in air flow through the radiator. The low rpm also causes 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.
Water Temperature Regulator
A water temperature regulator that does not open completely can cause above normal temperatures. To test the water temperature regulator, refer to Systems Operation, Testing And Adjusting.
Radiator Cap
A pressure drop in the radiator can cause the boiling point to lower. The lower boiling point could allow the cooling system to overheat. A pressure test of the cooling system may be used to check the cooling system pressure as well as the pressure cap relief valve. Ensure that the gasket sealing surface is clean and undamaged. If the cap fails the test, check the rubber seal on the cap as well as the operation of the pressure relief valve.
Radiator
Clean the radiator and flush the radiator. Check for debris between the fins of the radiator core which prevents free air flow through the radiator core.
A radiator that is undersized for an application will not effectively transfer the heat out of the cooling system. A radiator that is undersized will cause the engine to run at a temperature that is higher than normal. Make sure that the radiator is sized in accordance with the OEM specifications.
Faulty Water Pump
A water pump that has a loose impeller, an eroded impeller, or a 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.
Low Coolant Level
If the coolant level is too low, not enough coolant will circulate through the engine and the radiator. The decreased flow of coolant will not remove enough heat from the engine. This will cause the engine temperature to rise. Low coolant level is caused by the one or more of the following items:
- Leaks
- Faulty radiator cap
- Boiling of the coolant
- Incorrect filling of the radiator
Check the level of the engine coolant when the engine is cool. Ensure that the coolant can be seen at the low end of the filler neck on the top tank of the radiator.
Incorrect Coolant 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 mixture is incorrect, drain the cooling system, as needed. Put the correct mixture of water, antifreeze and coolant conditioner in the cooling system.
Air in the Cooling System
Air can enter the cooling system in different ways. The most common ways are improper filling of the cooling system and combustion gas leakage into the cooling system. Combustion gas can get into the cooling system through internal cracks, a faulty cylinder head, or a faulty head gasket. Air in the cooling system causes a reduction in coolant flow and bubbles in the coolant. Air bubbles insulate the coolant from the engine parts. This prevents the transfer of heat to the coolant.
Faulty Temperature Gauge
A temperature gauge which does not work correctly will not show the correct temperature. Verify the accuracy of the temperature gauge if the temperature gauge indicates that the coolant temperature is too high but other conditions are normal. Use a temperature gauge of known accuracy, or check the cooling system with the 4C-6500 Digital Thermometer .
Faulty Sending Unit
Some cooling systems use a temperature sensor in the engine that sends signals to a sending unit. The sending unit converts these signals to an electrical impulse which is used by a mounted gauge. If the sending unit malfunctions or the wiring has an open or a short, the gauge can show an incorrect reading.
Worn Hoses or Damaged Hoses
Faulty hoses with leaks can normally be seen. Hoses that have no visual leaks can collapse during operation. This will cause a restriction in the flow of coolant. Hoses become soft and/or get cracks after a period of time. Hoses must be replaced 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.
Air Inlet Restriction
An air inlet restriction can cause cylinder temperature to increase. This will transfer more heat to the cooling system. Check the air flow with a water manometer or a vacuum gauge. Connect the gauge to the engine air inlet between the air cleaner and the inlet to the turbocharger. Check the air flow with the engine at full load rpm. The maximum allowable air inlet restriction is 6.25 kPa (25 inches of H2O). If the indication is higher than the maximum permissible restriction, clean the filter element or install a new filter element. Check the restriction again. If the restriction remains too high, inspect the air inlet piping for obstructions.
Exhaust Restriction
An exhaust restriction can cause cylinder temperature to increase. This will transfer more heat to the cooling system. Make a visual inspection of the exhaust system. Check for damage to piping or for a faulty muffler. If no damage is found, check the exhaust system for back pressure from the exhaust (pressure difference measurement between exhaust outlet and atmosphere). Refer to Systems Operation, Testing And Adjusting, "Restriction Of Air Inlet And Exhaust". Check the system by removing the exhaust pipes from the exhaust manifolds. Operate the engine without the exhaust pipes. If the problem is corrected, the exhaust pipes have an obstruction.
Restriction of the Shunt Line
A restriction of the shunt line from the radiator top tank to the engine water pump inlet will cause a reduction in water pump efficiency. The result will be low coolant flow and overheating.
Restricted Air Flow Through the Aftercooler
A restriction of air flow through the aftercooler (if equipped) will transfer more heat to the cooling system. Check for debris or deposits which would prevent the free flow of air through the aftercooler.
Incorrect Fuel Setting
A high fuel setting causes a high heat rejection. If the engine cooling system is designed for a particular heat rejection and the heat rejection is changed the cooling system is no longer capable of cooling the engine. Ensure that the fuel setting is correct. Check and make necessary adjustments. Refer to Systems Operation, Testing And Adjusting, "Fuel Setting Check".
Incorrect Fuel Injection Timing
Ensure that the setting for the fuel injection timing is correct. Check and make necessary adjustments. Refer to Systems Operation, Testing And Adjusting, "Fuel Timing".