Bruce in Bangkok wrote:
I nearly went crazy trying to solve a similar problem after a fellow
ran aground on a mud bank. Finally discovered the heat exchanger tubes
full of mud after someone told me the boat had been aground and I
noticed there was no inlet strainer.

Also the heat exchanger tubes can get slowly clogged with marine buildup
so the engine eventually starts to run hot. The problem seems to just
appear suddenly so its easy to misdiagnose, and can appear in older
engines as a drop in oil pressure due to the higher engine temp. I am
working on an engine now that this has happened to. There are some
commercial products to clean this growth out. I have this heat exchanger
pickling in Rydlyme Marine solution which seems to be working, but I
suspect most of the products are the same.
Red