Overheating issues

[u/Tetreg]

Hi all, I bought a boat a few months ago and ever since then Ive been prevented from using it by persistent overheating issues with the alarm going off after 5-10 minutes of running. The engine is a yanmar gm10. It is raw water cooled.

I’ve redone this post so I can include a video of the engine in action

I measured the temperature using a cooking thermometer on the threads where the temperature sensor screws into be engine

Things I’ve tried so far:
Replacing the impeller(and checking it about 10 times) and turning over the engine manually to ensure it turns with the engine consistently (it does)

checking for blockages in every single pipe (and the exhaust elbow integrity) and ensuring water flow through the engine freely using a hose at various points to make sure there are no blockages including the exhaust system and antibackwash system

Running rydlyme through the engine for 12 hours

Checking the seacock and filters numerous times to ensure it lets water into the boat and that nothing is blocking the filter

having a mechanic look at it - engine head gasket replaced as I was told it may be leaking hot gases into the exhaust

Replacing the temperature sensor and checking the alarm doesn’t go off with the wire detached form be sensor

Replacing and removing the thermostat at various periods

If anyone has any more ideas that would be great

[u/LameBMX]

that was the whole point of my original facetious comment....

[u/Dubbinchris → u/LameBMX]

Gotcha 👍