Yanmar Overheating

[nknowland]

I had the same overheating issues and did everything mentioned above with no change. I finally replaced the heat exchanger and that did the trick (even though the HX had been serviced and pressure tested less than a year ago)._

[wsmurdoch]

In my case with a different Yanmar engine (3HM35F) I have several times found that the root problem was a lack of sufficient raw water flow.

I hold a bucket under the exhaust and catch the water coming out over a 10 sec period. I compare it to the amount coming out at the same rpm measured in the past when the engine was not overheating. I can also compare it to the amount shown in the Yanmar service manual for a much faster engine rpm ratioed down to the 2000 rpm that I use.

In one case I had broken a couple of impeller blades one of which was lodged in the discharge of the water pump">raw water pump. In a second the pencil zinc that protects my refrigeration condenser had broken off and plugged the raw water hose. In a third case (not caught by this method) the mixing elbow was nearly plugged off with carbon and rust.

I talked about it on "the other forum" Overheating - SailNet Community

[Steven UK]

Looks to me that the gauge is reading ten to fifteen deg higher than any part of the engine, check sender, gauge wiring.