High coolant temperature alarm; engine may derate or shut down; temperature gauge in red zone.

Safety: Do not open the coolant cap on a hot engine. Allow it to cool completely.

• Check coolant level: After cooling, inspect the expansion tank and top up with the correct Volvo Penta-approved coolant mix if low. Investigate for external leaks at hoses, clamps, radiator, and water pump.
• Inspect radiator/heat exchanger: For air-cooled radiators, clean fins with low-pressure air or water, blowing opposite normal airflow. For heat exchanger systems, check for marine growth or scaling and clean per Volvo Penta procedures.
• Verify fan and belts: Ensure the cooling fan is intact and belts driving the coolant pump and fan are tight and not slipping. Replace worn belts.
• Check thermostat operation: If overheating persists, remove the thermostat and test it in hot water to see if it opens at the specified temperature. Replace if stuck closed or sluggish.
• Inspect coolant pump: Look for weep holes leaking or wobble at the pump shaft. A failed pump must be replaced.