My Yanmar 2GM was overheating because I could not get sufficient raw
seawater to flow through the heat exchanger. I cleaned the exchanger,
cleaned all lines leading to and from it, cleaned the raw water
strainer, cleaned growth from the water intake. I was able to blow
air thru from the top of the intake to verify it had no blockage. It
would start to pump and then soon be only a trickle. Replaced the
pump impeller twice too. WTF?
Finally, after months of screwing with it, I took off the raw water
seacock (problematic cuz she is in the water) and between the seacock
and hull fitting, found a piece of shell that would act as a one-way
valve when it got sucked into the seacock. I could blow downward thru
it no problem and it would initially flow upward too but it would then
lodge in the seacock blocking it.
SO, if you have raw water flow problems, you might check for this.