Yanmar Hi Temp
It would certainly help to know which engine you have, and whether or not it is fresh water cooled. But the previous post is correct. One of the very first things to check is the raw water impeller. And check it closely. There have been some Yanmar impellers that spin the center hub, and unless you check it very closely, will not be noticable. I know this from experience. I now buy Johnson impellers. My Yanmar distributor carries them and they are identical to the Yanmars, with the exception that the pin goes all the way through the impeller on the Johnsons, and the Yanmar is bonded some way. If fresh water cooled, the heat exchanger is pretty high on the list of things to check.
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