Probable Causes
- Low coolant level
- Air in coolant
- Water pump
- Environmental conditions
- Shunt line restriction
- Radiator or heat exchanger
- Water temperature regulator
- Coolant temperature sensor
- Engine coolant flow
- Exhaust restriction
- Excessive load
- Combustion gas in the coolant
Recommended Repairs
Low Coolant Level
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Pressurized System: Hot coolant can cause serious burns. To open the cooling system filler cap, stop the engine and wait until the cooling system components are cool. Loosen the cooling system pressure cap slowly in order to relieve the pressure. |
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Note: Low coolant level can be the result of overheating rather than the cause.
Check the coolant level.
Run the engine to operating temperature.
Inspect the cooling system for leaks. Check for the presence of coolant in the engine oil. This would indicate an internal coolant leak.
Determine whether the leak occurs before the engine overheats.
Add coolant, if necessary. If leaking is found, make the necessary repairs.
Air in Coolant
Air can enter the cooling system if the pressure cap is not operating properly. Check the operation of the pressure cap. Replace the pressure cap, if necessary.
If the coolant has been changed recently, ensure that the air has been purged from the cooling system.
The supply pressure to the water pump must be sufficient in order to prevent cavitation. Measure the supply pressure at the inlet to the water pump.
Water Pump
The engine will overheat if the water pump is not operating properly. Measure the coolant pressure at the outlet of the water pump. Make sure that the water pump is in good condition.
Environmental Conditions
Determine if the ambient air temperature is within the design specifications for the cooling system.
Ensure that the engine's exhaust does not heat the radiator or the heat exchanger.
Check for high inlet air temperature.
Determine the cause of the high air temperature. Make corrections, when possible.
Shunt Line Restriction
If the cooling system is equipped with a shunt line, check for a restriction in the line. A restricted shunt line can cause cavitation in the water pump. Remove the restriction or replace the shunt line.
Radiator or Heat Exchanger
Measure the coolant temperature at the inlet to the engine.
Radiator
If the engine is equipped with a radiator, check the fins of the radiator for obstructions. Check the fan for proper operation.
If the radiator fins are obstructed, clean the fins. If the fan does not operate properly, make the necessary repairs.
Heat Exchanger
If the engine is equipped with a heat exchanger, check for sufficient flow and temperature of the cooling water through the heat exchanger. If the flow of cooling water through the heat exchanger is insufficient, determine the location of the obstruction.
Water Temperature Regulator
Check the water temperature regulators for proper operation.
Replace the water temperature regulators, if necessary.
Coolant Temperature Sensor
Check the reading of the coolant temperature on the Caterpillar Electronic Technician (ET). The temperature should rise steadily as the engine is warmed. Ensure that the temperature is reasonable.
If the reading on Cat ET for the coolant temperature is not reasonable, troubleshoot the circuit and the coolant temperature sensor. Refer to Troubleshooting, "Engine Temperature Sensor Open or Short Circuit - Test".
Engine Coolant Flow
Insufficient coolant through the engine can be identified by checking the coolant temperature at various points in the cooling system.
During normal operation, measure temperatures at several different points in the cooling system. This will help to identify possible locations of restrictions.
If a buildup of deposit in the cooling system is suspected, clean the cooling system.
If the flow of coolant through the engine is not sufficient, determine the cause of the obstruction. Make necessary repairs.
Exhaust Restriction
Check the back pressure of the exhaust system. Refer to the engine's Technical Marketing Information.
If the back pressure exceeds the specifications for the engine, determine the cause of the excessive back pressure. Make the necessary repairs.
Excessive Load
Make sure that the load is not excessive. Reduce the load. If necessary, disengage the driven equipment and test the engine for high coolant temperature.
Combustion Gas in the Coolant
Check the cooling system for combustion gas. This can be identified by small air bubbles in the coolant during engine operation. Identify the source of the combustion gas. Make the necessary repairs.