Liquid-cooled Guardian standby generator shuts down during run with HIGH COOLANT TEMP or HIGH ENGINE TEMP alarm.

Safety first: Turn the controller to OFF, open the main breaker, and allow the engine to cool completely before opening the coolant cap. Hot coolant can cause severe burns.

• Check coolant level: Once cool, remove the radiator cap or reservoir cap and verify coolant is at the proper level. Add the correct coolant mixture recommended by Guardian if low.
• Inspect radiator and fan: Check the radiator fins for dirt, leaves, or cottonwood fluff. Clean gently with low-pressure air or water from the back side. Verify the electric radiator fan spins freely and runs when the unit is operating.
• Check fan fuse and wiring: Locate the fan fuse and relay in the Guardian control panel. Replace blown fuses with the correct rating and inspect wiring to the fan motor for damage.
• Temperature sensor: Inspect the coolant temperature sensor connector for corrosion or loose fit. A faulty sensor can falsely indicate overheat.
• Test run: After corrections, reset the alarm and run the generator under load while monitoring temperature. If overheating recurs, contact a Guardian service technician to pressure-test the cooling system and verify water pump operation.