Re: Onan shuts down under load without shutdown codes



Guessing from thousands of miles away.

The shutdown is because the block is too hot. 

Normally it should be about 80C under load and warmed up. However, the exhaust elbow is at the correct temperature. My guess is that the coolant is not circulating as it should, and therefore not cooling the block. The seawater side seems to be functioning correctly, but not the coolant side. That could be a number of things including the coolant (captive) pump, a loose fan belt on the captive pump, a stuck thermostat, an obstruction somewhere in the coolant path.

I would start with the thermostat. If you do not have a spare, you can temporarily remove it until you have one. You will likely need some PermaTex-type gasket material because those gaskets usually tear.

CW Bill Rouse Amel Owners Yacht School
Address: 720 Winnie, Galveston Island, Texas 77550 
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On Fri, Aug 14, 2020 at 1:28 PM Mark Pitt <mark_pitt@...> wrote:
I installed a new flow sensor that I had in my spares.  I also replaced the impeller.  The existing impeller did not look too bad but it appeared that one vane had adhered to the impeller hub, perhaps from overheating.  I opened the cooler and found no obstructions. I also examined the hose segments from the raw water pump to the cooler and found no obstructions.

I then ran the generator under a load of 13.5 amp.  When the engine block temperature reached 103C degrees, I shut the generator off.  The exhaust elbow never topped 52C degrees.  So this appears to be a problem on the cooling side.  The cooler itself is a less than two year old "Mr. Cool" that has been in service for at least 600 hours without problem. When I put the boat away for the winter last October, there was no hint of problem.  I fully winterized it at the time.


Mark Pitt
Sabbatical III, SM #419, Rhode Island, USA

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