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Onan 16 hp twin, blowing oil

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#1 jwilliams1130 OFFLINE  



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Posted January 05, 2011 - 10:58 PM

I have an Onan twin 16 hp on a Sears Suburban tractor. I just got it and know nothing about Onan engines. It is blowing oil up thru the hose that goes to the air cleaner. Could it be the oil pressure relief valve is not working correctly, or is it something else?
Any ideas would be appreciated.


#2 MH81 ONLINE  


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Posted January 05, 2011 - 11:10 PM

Does the vent look like it's been off before? Some of those covers can be installed upside down & cause this.

It could also be a plugged port or drain hole near there.
I'm not very familiar with the positive pressure systems. Wish I could help more.

#3 jdcrawler OFFLINE  



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Posted January 05, 2011 - 11:34 PM

The 16 HP Onan engine that I put in my home made tractor was doing the same thing when I first started it up.
It turned out that the very top ring was broken on both pistons.




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Posted January 06, 2011 - 12:10 AM

If it's doing any more than a light mist I would go straight to a compression check. Odds are you've got blowby on the rings like jd said.

#5 olcowhand OFFLINE  


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Posted January 06, 2011 - 09:38 AM

I would do a compression test, & if within specs (90psi or higher, up to 110psi or so), then check the reed in the crankcase breather assembly. If the reed is in proper shape, then be sure there are no leaks in the crankcase itself, such as a bad oil dipstick seal. Any leak allowing air in can overwhelm the breather causing excess oil to pass through it.