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

Tap to mark as ruled out

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

8 steps · ~60 min

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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