I had some engine work done over the last two months, and everything was finally completed and put back together at the yard yesterday, with one problem: the engine was operating at the high end of the normal 165-195° range. The yard check the raw water impeller and it was fine, there was flow out the exhaust, so they suspected the heat exchanger.
Since it is literally a few hundred yards to my slip, I decided to take her home and see if I could fix the problem myself. Started off fine, water coming out of the exhaust, the temp rose steadily to about 160-180, but after a few minutes shot up to 220 - obviously out of range. By then I was at the slip, so I cut the engine and glided in. Total time yard to slip maybe 3-5 minutes.
First things first, I checked the raw water impeller myself - very small crack in one of the vanes, but other than that it was fine (meaning no missing pieces - but it will be replaced anyway).
I have a hot water heater and a reservoir in the lazarette; it was completely empty, and is usually at least half full. So, there may not have been enough water/AF added into the fresh water circuit when it was put back together.
I removed the heat exchanger and flushed it out with fresh water; there was a fair amount of silt/dirt on the raw water side. When I took off the end cover/gasket, there was some crud but no noticeable scaling (at least not to me... the PO had the HE serviced about 2 years ago by a local radiator shop). Then I looked closer - at least two holes on the raw water intake side were plugged with black plastic, with some other loose pieces of plastic and zinc remnants. I gently ran a wire down each tube and unplugged some junk from the other end, then flushed it out through the zinc mount. All told, here's just some of what came out, mostly on the raw intake side. The Yard was pretty sure this was causing enough obstruction of the raw water flow to cause the overheating:
Here's a shot of the tubing - does that appear to be in pretty decent shape? I will probably drop it off for servicing this week:
Tomorrow if I get a chance I'll check the thermostat and mixing elbow, any other suggestions?