Boat engine temperature alarm: secure the boat and find the cooling fault

Stop before a fault becomes a breakdown

Throttle back, make sure the boat is safe and follow the engine's alarm instructions. If no cooling water is coming out, or the engine is genuinely hot, shut it off. Running on can ruin the engine. Don't restart just because the alarm has gone quiet. The fault is probably still there. If you can't get the cooling working safely, call for a tow.

Never open a hot cooling system that is under pressure. Keep hands and tools away from belts and the propeller. Then start with the troubleshooting for your model.

Which cooling system do you have?

An outboard is cooled by raw water. Many inboards have a closed system with coolant that is in turn cooled by raw water in a heat exchanger. Others run directly on raw water. So an inboard can have a fault on the raw water side, the coolant side or both.

The tell-tale stream on an outboard says something about the cooling. A blocked tell-tale can be weak even though water is circulating in the engine. A good stream can be there even though something else is wrong. The alarm and the manual count for more than the stream.

Start with the waterway

1. Stop the engine. Check whether the intake is blocked by seaweed, plastic or silt.
2. On inboards: make sure the seacock is open and the raw water strainer is clean. Close the seacock before opening the strainer, as the installation requires.
3. Check hoses and connections for leaks. A leak on the suction side can draw in air.
4. If there is still no water, remove the impeller. If vanes are missing, find the pieces.
5. Refit strainer lids and valves correctly before you test start.

Read the impeller guide and find the right part under spare parts. A raw water pump must never run dry.

When the raw water system seems to be working

Let the engine cool down completely. If it has a closed system, check the coolant level. Top up with coolant of the specification given in the manual. The thermostat, circulation pump, heat exchanger and exhaust parts may need a workshop. Sometimes it is just the sender playing up, but only assume that once real overheating has been ruled out.

Note whether the temperature rises only under load or at idle as well. Write down the alarm text, the rpm, the time and what happened beforehand. Then the workshop won't have to ask you for another test run.

When you hand over to the workshop

Stop wrenching if there is a major leak, steam or mechanical noise, or if the alarm returns after a simple fix. If the engine has run hot for a long time, impeller pieces are missing or you can't reach the system safely, have a mechanic look at it. An acknowledged alarm says nothing about the condition.

Look up the engine and serial number in the engine catalogue and contact a boatyard. Ask them to find the root cause and do a test run after the repair. If only the impeller is replaced, a blockage further in may remain.

Frequently asked questions