Generator shuts down; Code 24 displayed indicating high engine temperature

Safety first: Allow the generator to cool completely before opening any coolant caps. Hot coolant under pressure can cause burns. Disable auto-start.

• Check coolant level: Inspect the coolant level in the expansion tank and radiator (if accessible). Top up with the correct coolant mix specified by Onan. If low, inspect for leaks at hoses, radiator, and water pump.
• Inspect fan and belt: Verify that the cooling fan turns freely and that the belt is intact and properly tensioned. Replace worn or broken belts.
• Clean radiator and air passages: Remove debris, leaves, and dust from the radiator fins and generator enclosure air inlets. Use low-pressure air or water; avoid bending fins.
• Check coolant temperature sensor: Inspect the sensor wiring and connector. If the engine is not actually overheating (verified with an infrared thermometer) but Code 24 appears, replace the coolant temperature sensor.
• Thermostat and pump: If overheating persists with proper coolant level and airflow, the thermostat may be stuck closed or the water pump may be failing—have a technician test and replace as needed.