Re: randomly occurring increases of engine temperature


Raw Water Pump Chamber Wear:
That is an interesting point. I searched for the diameter of new raw water pump chambers and could not find any dimensions for the Onan/Sherwood 702 pump which is on most Onan generators, the Volvo engines, and the Yanmar engines. I think this may be something that an owner would want to know. If any of you happen to have new pumps as a spare, please measure the inside diameter of the raw water pump chamber and reply.

Impeller Blade Wear at the Tip of the Blade:
I have never measured the wear to the inner wall, but have measured wear to the impeller blade tips and found a reduction in diameter of a little more than 2mm. This wear happens for 2 reasons: Hours of use and the cleanliness of the inner wall. The inner wall of a seawater pump will become crusty to the touch from the buildup of minerals. The more abrasive the inner wall is the more wear. The inner wall should be cleaned each time an impeller is changed with a combination of 600 grit wet/dry and Scotchbrite pad.

Sadly, many people think that impellers only need to be replaced when the blades tear off and the engine overheats. 

CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
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On Fri, Sep 10, 2021 at 10:51 PM Trevor Lusty <trevlusty@...> wrote:
       I had a similar problem. with the Yanmar engine in my SM for almost a year which drove me mad. Finally I bought a new sea water engine pump more out of desperation than discovering the actual fault.
When fitting the new pump I had the old and new pumps sitting together in the cockpit.  I thought I was imagining it, bit when I checked the old one with my callipers the chamber that houses the impeller was almost 2mm wider than the new one from wear. 
Fitted the new pump and the temperature returned to and stayed at 80C.
Trevor Lusty

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