I have a 24' Grady-White powered by a 225HP Mercury OffShore (1994 ?) I had an overheating problem that would occur at lower rpms ( approx 1000 rpm) but would clear wheni got going. It would also occur when i got on plane (about 3500rpm) The alarm would go off, I'd stop the engine for a few minutes, the alarm would clear and then I'd resume. I'd be ghoing along OK for a while on plane, the temperature would be low (half scale) and then all of a sudden it would rise and alarm go off. My mechanic changed the thermostats, poppits, diaphragm and completely replaced the water pump (not rebuilt). The engine no longer overheats when run full out, but the temp gradually rises and the alarm still goes off when I'm running at approx 1000rpm or below. Any ideas what's going on??
I might add that the spark plugs are burning clean and the last compression check didn't reveal anything out of the ordinary.
I might add that the spark plugs are burning clean and the last compression check didn't reveal anything out of the ordinary.