TL;DR
Engine overheating is most often a plugged radiator or failed thermostat. Check coolant level, inspect the radiator core for dust packing, and test the thermostat before running again.
What you might see
- coolant temperature gauge in red zone
- engine derate or automatic shutdown
- steam from the engine compartment
- coolant loss between services
Likely causes
Radiator core plugged with mineral dust reducing airflow across the cores
Failed thermostat stuck closed preventing coolant circulation
Coolant leak from a hose, fitting, or head gasket reducing coolant volume
Cooling fan drive fault reducing fan speed
Required tools
- Coolant system pressure test kit
- Thermostat test container and thermometer
- Low-pressure compressed air or garden hose
- LOTO kit
Safety first
- Never open a pressurized coolant cap on a hot engine. Scalding steam will eject.
- Lockout the engine start before performing any work in the engine compartment.
Procedure
- 1
Shut down the engine immediately when the temperature gauge enters the red zone.
Warning: Never open the coolant cap on a hot engine. Wait at least 30 minutes and use a rag over the cap to release pressure slowly. - 2
After cooldown, check the coolant level in the expansion tank and the main radiator. Low level confirms a leak.
- 3
Inspect radiator inlet and outlet hoses for cracks or soft spots from internal collapse.
- 4
Inspect the radiator core face for dust or mud packing. Clean with low-pressure compressed air or water from the engine side outward.
- 5
Check the cooling fan belt tension and condition if belt-driven. Check the hydraulic or electric fan drive if applicable.[1]
- 6
Test the thermostat by removing it and placing it in a container of hot water with a thermometer. It should open fully below the rated opening temperature printed on the thermostat body.
- 7
If the thermostat tests good, pressure-test the cooling system with a hand pump tester to find the leak source.
- 8
Repair leaks and replace the thermostat if suspect. Refill with the correct coolant mixture before restarting.
Sources
Caterpillar CAT 6060 / 6090 Hydraulic Mining Shovel / Excavator general technical documentation, Caterpillar
Caterpillar large diesel engine cooling system maintenance, general cooling system inspection procedures (general)
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