Engines
Why does my engine overheat after about 20 minutes?
A delayed overheat usually means reduced cooling flow rather than no flow: a partly blocked strainer or intake, a tired impeller, scaled heat exchanger, or a slipping belt. Stop the engine, check for water at the exhaust and look at the raw-water strainer before running again.
If it overheats immediately, something is fully blocked or the impeller has failed. If it takes twenty minutes, the engine is shedding some heat but not enough — often a heat exchanger furred with scale, a partly weeded intake, or an impeller with a couple of vanes missing that have lodged downstream.
Running on regardless is what turns a cheap job into an expensive one. Overheating cooks the exhaust elbow, hoses and eventually head gaskets. Shut down, let it cool, and check the obvious items before restarting.
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