Fuel in Oil – Onan Generator

[Matt Lyman]

I just got my oil sample back on my 9KW Onan generator and it unexpectedly had a huge jump in the % of oil in it (4%).

The generator had sat for 5-6 months without being ran, could this have caused the increase of fuel in the oil? 

There was a lot of oil on the water when I fired it up, which dissipated completely after running it for 10 min. 

Other ideas? I’m seeing other possible causes as:

• Lift pump
• Injectors
• Piston seals

Thanks for the hep!

Topic

[Rob Schepis]

Here’s the report re-uploaded as a jpeg image.

Does this genset run with a good amount of load on it?

[Gene Fuller]

Your oil test page cannot be loaded.

PDF files will not open with a click in the same manner as an image. It is necessary to right-click and select “open with”, or “open in a new tab”, or even download.

The PDF attachment is this case is fine. The problem is in getting the correct sequence to open it.

1 user thanked author for this post.

Rob Schepis

[Clark Leighs]

Your oil test page  cannot be loaded.

Piston seals not likely unless an injector is leaking dripping fuel into a cylinder allowing the fuel to run past and get to the crankcase.

A lift pump can do this depending upon how it is driven which I don’t know.  You will need to look or use the part dwg.   If it is an electric pump then highly unlikely.   If it is a type of diaphragm  pump operated by a lever from the camshaft then it is a possibility.    Diaphragms can fail and leak and have done this.

Injectors can leak at O rings feeding the oil system with fuel.    Also if the return fuel line is under the valve cover they have been known to leak from vibration loosened fittings, cracked return tubing and so on.      

[Author]

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