Ross,
Had a similar issue this year during a trip to Catalina Island from San Diego. Engine was running hot but not overheating so I decided to just lower my RPMs and nurse her to Catalina where I could trouble shoot the problem. I started by diving under the boat and checking the through hull, I then checked the sea strainer and impellor. I found that all was OK so I figured it must be the heat exchanger. I removed the end caps and all seemed ok so I put it all back together but the engine still ran hot. I decided to go for it and remove the heat exchanger to get a better look, and also check all the hose for blockage. Its a good this I removed it because it turned out that a majority of the small tubes where totally blocked with calcification. I was able to find an old antenna whip at the local repair barge and used it as a ramrod to clean out every tube. I also soaked the unit in some muriatic acid that I got from the hardware store, that really cleaned out every last bit of corrosion. I reassembled, fired up the motor and was good to go with engine temps back at normal range. Let me say that our trip home was a lot less stressful that the trip there.
Had a similar issue this year during a trip to Catalina Island from San Diego. Engine was running hot but not overheating so I decided to just lower my RPMs and nurse her to Catalina where I could trouble shoot the problem. I started by diving under the boat and checking the through hull, I then checked the sea strainer and impellor. I found that all was OK so I figured it must be the heat exchanger. I removed the end caps and all seemed ok so I put it all back together but the engine still ran hot. I decided to go for it and remove the heat exchanger to get a better look, and also check all the hose for blockage. Its a good this I removed it because it turned out that a majority of the small tubes where totally blocked with calcification. I was able to find an old antenna whip at the local repair barge and used it as a ramrod to clean out every tube. I also soaked the unit in some muriatic acid that I got from the hardware store, that really cleaned out every last bit of corrosion. I reassembled, fired up the motor and was good to go with engine temps back at normal range. Let me say that our trip home was a lot less stressful that the trip there.