Cooling Problem

[ivanhoe]

Last Saturday Myself,wife, and daughter went fishing in our boat. The mercruiser 4cyl. would run to almost 1/2 throttle, then overheat. After an hour or so it cooled down enough to go again. run for bit and heat-up again. I hope someone can tell me what could be the problem is. or how to ck the problem. I have some mechanic knowlege,but not to smart with out-drives.

 

[Bt Doctur]

start with a new water pump in the lower unit .Most times running hot at rpm and then cooling down with a lower rpm indicates a impeller/flow issue

 

[bondo]

Ayuh,.... Agreed,.... In any over-heat situation, rebuild the raw water pump 1st,....