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Old 01-22-2019, 05:51 PM   #1
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Strange, Onan Gen quits after 30 minutes

This is a model from the 80's in my Marine Trader. Oil pressure is normal, not overheating, full of oil, but shuts down almost exactly 30 minutes later. Ideas? Thanks.

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Old 01-22-2019, 07:11 PM   #2
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While it is running is it putting out power properly? Do you have a manual with troubleshooting outline?

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Old 01-22-2019, 09:45 PM   #3
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Since the time is uniform, probably a sensor or solenoid that fails when it becomes heated. I would temporarily bypass the shutdown sensors (oil pressure, coolant temp, exhaust overheat and any relays that they control) and see if that makes a difference. Next I would probably replace the fuel solenoid in the top of the injector pump. If you do this don't screw with anything else on the pump.
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Old 01-22-2019, 09:47 PM   #4
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Model of ONAN? Otherwise we are all just guessing.
Almost forgot... Welcome Aboard!
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1984 Monk 36 Hull #46
Currently in Cape May NJ
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Old 01-23-2019, 07:18 AM   #5
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Mr. J. Welcome aboard. I had a similar issue (time dependent) with one of our Lehmans. Ran fine for a certain length of time then quit. The cause was a collapsing rubber fuel line. There was enough meager flow and enough fuel in the Racor to allow about 40 minutes of run time but then she done quit. One more thing to consider.

Like anything rubber, fuel lines have a finite lifespan and although they may appear fine on the outside, they can de-laminate allowing the inner rubber liner to collapse under lift pump vacuum thus limiting or shutting off sufficient fuel supply. Not as uncommon as one may think...
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Old 01-23-2019, 07:59 AM   #6
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With all the constants in a closed/open system, I had the same issue. Engine would start up run normal for a set time and shut down. I had a trash, old water pump in an elbow of the coolant system. I cleaned that out after I replaced all the water pump (raw water) circuit. Note: a short time later the engine ran funny, surging and not leveling out, that ended up being a short in the generator that was causing lots of load under a no load condition. Ended up buying a newer generator.
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Old 01-23-2019, 11:35 AM   #7
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My guess would be a shut down solenoid or a safety sensor such as oil, overheat.
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Old 01-23-2019, 02:05 PM   #8
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The oil pressure switch, if the diaphragm has a hole, will allow oil to cross and after a while, the switch will open.
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Old 01-24-2019, 10:44 AM   #9
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Check the electric fuel pump, it failed on mine and is a known issue. You will probably find diesel inside the pump motor as the seals fail. An aftermarket pump is much cheaper than an Onan pump....
Don't believe everything that you think.
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Old 01-24-2019, 11:03 AM   #10
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One post and gone....

Don't put too much brain power in this.
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Old 01-24-2019, 02:29 PM   #11
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Thank all of you for your input. I will check all of your suggestions as soon as I arrive at my boat. This is my first foray in the forum, I'm very impressed!

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