TL;DR

Generator overheating is almost always low coolant, a blocked radiator, or a failed water pump. Check coolant level first, then radiator cleanliness, then thermostat and water pump operation.

What you might see

coolant temperature gauge above normal operating range
EMCP high-temperature shutdown alarm
coolant overflow tank overflowing
coolant level in expansion tank dropping

Likely causes

Tap to mark as ruled out

Coolant level low from a leak or evaporation loss
Radiator core blocked with dirt, debris, or insects reducing cooling airflow
Failed thermostat stuck closed, preventing coolant circulation to the radiator
Water pump impeller worn or cavitating, reducing coolant flow

Required tools

Multimeter or IR thermometer for coolant temperature spot checks
Replacement thermostat (correct temperature rating)
CAT ELC or DEAC coolant (correct specification for C-Series)
Hose clamp pliers

Safety first

Never remove the radiator cap on a hot engine. The pressurized coolant will erupt and cause serious burns.
Diesel engines can be very hot after running. Allow at least 30 minutes cooling time before touching the engine block, radiator, or exhaust components.

Procedure

7 steps · ~45 min

1
Stop the generator and check the coolant level in the overflow tank and the radiator. Do this only when the engine is COLD.
Warning: Never open a hot radiator cap. The cooling system is pressurized when hot. Open the cap only when the engine is cold or use a rag to slowly release pressure.
2
If coolant is low, inspect for external leaks at the hose connections, the radiator, the water pump seal, and the head gasket (white smoke from exhaust indicates a head gasket leak).
3
Inspect the radiator from the front. If the fins are clogged with debris, clean with low-pressure water or compressed air from the engine side outward.[1]
4
Check that the cooling fan is running at the correct speed. On belt-driven fans, inspect the belt for wear and proper tension.[1]
5
With a cold engine, start the generator and monitor coolant temperature. If temperature rises past the normal range without the upper radiator hose becoming hot, the thermostat may be stuck closed. A stuck-closed thermostat is confirmed when the lower hose stays cold while the upper hose gets very hot.
6
Replace the thermostat with a new unit of the correct temperature rating for the C-Series engine. Drain and flush the cooling system and refill with the correct CAT coolant specification.[1]
7
If the thermostat is normal and coolant flow is present but temperature still rises, test the water pump flow rate. Low flow indicates impeller wear requiring pump replacement.

Sources

Caterpillar C-Series Generator Set Operation and Maintenance Manual, Caterpillar Inc.
Caterpillar C-Series generator set operation and maintenance manual, cooling system maintenance and thermostat replacement (general)
View source

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