In article ,
"Jeffrey P. Vasquez"
wrote:

Hello all,

I recently did a standard maintenance replacement of a raw water impeller
on a Yanmar 2GM diesel. Everything seemed straightfoward, part for part,
no leakage, everything went back together straight away and test runs at
the dock were nominal.

However, during a move to a new slip the engine alarm went off. A
subsequent check revealed nothing. Took the boat out and ran the engine
for a good hour and there were no issues. The second time out the engine
alarm went off again after about the same duration of running time as the
incident during the move to the new slip.

This time there was no curing it. I dismantled everything upstream and
downstream of the water pump and it appears there is no flow through the
water pump even though everything appears to be functioning exactly as
it's supposed to. The impeller is fine, the belt tension and pulley
function are fine and there are no blockages from the through-hull to its
egress.

The boat is a 1989 S2.

I am stumped. Any suggestions would be infinitely appreciated.

Thanks,

One thing to check isif the shaft that drives the impeller is in one
piece. I had a JABSCO where the shaft was made in two parts that were
pressfit together. Water leaked thru a failed seal and corroded the
shaft connection to the point that the pressfit connection failed.
Pully turned, but impeller didn't. I found it by turning over the
engine with the pump faceplate off and watching the impeller itself.

Bruce in alaska
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add a 2 before @