Author Topic: Onan 12.5 Generator Leaking Oil  (Read 354 times)

Don White

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Onan 12.5 Generator Leaking Oil
« on: December 05, 2021, 07:14:10 PM »
I recently had my generator serviced.  I started the generator up a few days after getting the coach back.  The generator started up fine and ran very smooth and quiet.  After running it for an hour I shut it down and the generator immediately started leaking oil.  It did not leak while it was running.

Any suggestions on what could be happening?  Could it be the oil was over filled?  What kind of damage can an overfill situation cause?  Any other possible causes? 

Thanks.
Don White
2006 Marquis Jade IV C13
2019 Jeep Wrangler
Hydralift
2006 HD Fat Boy
1997 Safari Serengetti

Eric Maclean

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Re: Onan 12.5 Generator Leaking Oil
« Reply #1 on: December 05, 2021, 07:47:26 PM »
Don
The first thing to check is the oil level on the dip stick for over full or under full condition
The other things to checklist the oil drain plug and oil filter for seals it is possible the old oil filter seal ring is still on the filter housing resulting in a double seal condition this would cause your issue
Or the drain plug may be loose or a damages gasket on the plug causing the leak.

Hope this helps
Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.

Don White

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Re: Onan 12.5 Generator Leaking Oil
« Reply #2 on: December 05, 2021, 10:01:06 PM »
Hi Eric,

Apologies, I should have included in my first post that I did check the dip stick.  It is halfway between what I assume are the cold and hot fill marks on the dip stick.  There is no visible sign of leaking around the oil filter, oil fill tube, or dip stick.  I will check the drain plug tomorrow.  I would think if it were the drain plug it would be a constant leak, not just a momentary leak when I shut the engine down that is maybe a cup or 2 in volume and then stops.  Am I missing something?
Don White
2006 Marquis Jade IV C13
2019 Jeep Wrangler
Hydralift
2006 HD Fat Boy
1997 Safari Serengetti

Mike Shumack

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Re: Onan 12.5 Generator Leaking Oil
« Reply #3 on: December 06, 2021, 02:03:42 PM »
On my 10KW Onan generator, there is a foam-like gasket between/around the oil drain plug that sort of seals (loose term) the oil pan to the gen box structure.

 If the mechanic spilled some oil while changing the filter, it could take some time for it work its way out past that foam gasket. If that is the case the leak will stop after a short while.

Eric Maclean

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Re: Onan 12.5 Generator Leaking Oil
« Reply #4 on: December 06, 2021, 08:37:26 PM »
Mike makes a good point it may also hold the oil in a puddle in the gen set box with the wind that the generator fan produces and once the gen set is shut down then the oil will is no longer he!d at bay by the fans wind and round to a low spot and out .

I'd keep an eye on the oil level to see if it drops with operation over a period of time

You could open the bottom service hatch and look around with a light for the oils origin maybe even wipe it dry
Be careful using brake clean or another solvent in the gen box enclosure as most solvents are flammable.

Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.