Generator stops, and the controller shows AL03, indicating a high coolant temperature alarm/shutdown.

Safety first: Allow the generator to cool completely before opening the radiator cap. Hot coolant under pressure can cause severe burns.

• Check coolant level: Inspect the expansion tank and radiator (when cool). Top up with the correct coolant mixture recommended for SDMO engines. If the level was very low, inspect hoses, the radiator, and the water pump for leaks.
• Clean radiator and airflow path: Remove debris, dust, and insects from the radiator fins using low-pressure compressed air from the engine side out. Ensure the SDMO canopy louvers and air intake/exhaust paths are not blocked.
• Inspect fan and belt: Verify that the cooling fan rotates freely and that the belt has proper tension and no cracks. Replace a worn or broken belt with the correct size for the SDMO engine model.
• 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 it if stuck closed or sluggish.
• Verify coolant temperature sensor: Inspect the coolant temperature sender connected to the SDMO controller. A faulty sensor can trigger false AL03 alarms; replace it if readings are inconsistent with the actual engine temperature.