Re: How hot...overheating?
Is this a theoretical question or is this something that happened to you or someone you know? I'm assuming this is a water cooled motor? Although air-cooled engines can overheat, I don't think it's as common. I'd have to say the first question is, can you turn the flywheel by hand after the motor has stopped. If it's hot enough, it's possible the piston rings have seized to the cylinder walls and it's going to take a lot of work to get it running again. At the very least, if the motor still turns, you cooked the gaskets and gasket compound, discolored the paint and shortened the life of the piston rings somewhat. On most motors under 10 HP there should be a tell-tale stream of water coming out as you are operating it. (If you're in a test tank make sure the water pump impeller is immersed). If there's no water coming out, or if the cylinder head is too hot to put your hand on shut it down immediately! A normally operating motor should be warm to the touch, but not painfully hot. Most modern outboards with a thermostat open up around 140-degrees to give you a rough idea of how warm the cooling water should be. Anyway, that's been my experience.
Hope this helps!
Bob P.
