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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 15180
Experience:  Certified on Onan and Generac generators
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I have a onan p216 and I am getting oil spitting from the

Customer Question

I have a onan p216 and I am getting oil spitting from the backside of the fuel pump
Submitted: 7 years ago.
Category: Small Engine
Expert:  Hank F. replied 7 years ago.


What is the full model number of your engine?

There are more than 1 version of the P216.


Customer: replied 7 years ago.
HI, the model #is P216G 17112BOE...I checked the compression and its about 118 on one cylinder and about 119 on the other, I checked the packing on the riser tube from the crankcase for obstructions and there were none, the engine only has 498 hours on it, its a 2004 model, and has no smoke in the exhaust that I can see, and runs great other than the small amount of oil spitting from the back of the fuel pump
Expert:  Hank F. replied 7 years ago.

On the back of the fuel pump is a piece of hose that is either 7" or 10 1/4" long, depending on which block this engine uses. This is the fuel pump pulse line, and is where the oil is coming from.


Only 3 things will cause oil to get into this line:

1. The engine is/was overfilled with oil.

2. Too much crankcase pressure, caused by either packing in the breather being full of oil (simply clean the packing in solvent), or bad rings allowing exhaust blow-by. The cylinders can show good compression but still be allowing blow-by. Only a leak down test can determine if the rings are at fault.

3. The unit has been operated on too steep of a slope, allowing oil to get into the line.


Check the oil level to ensure it is not overfull.

Remove the pulse line from the engine and thoroughly clean it out.

If oil still continues to get into the line, you will probably need to have a leak down test performed on the engine to determine if the rings are at fault.


Customer: replied 7 years ago.


HI, on top of the packing is a removable cap that has 4 holes in it, 3 of which have a, what looks to be a neoprene ball in it, and one of the holes is open with no ball in it, could this be the problem? the packing looks as good as new, and I just changed the oil and put 1.75 qts including the filter which is what the manufacturer states is the correct quantity.... I have no way of performing a leak down test, if it is indeed the rings, how hard is it to replace them?

Expert:  Hank F. replied 7 years ago.

One of the balls missing would not cause this. It's when the balls stick and can not move that would cause it.

Even though the book says 1.75 Qts, you still need to go by the full mark on the dipstick. Make sure the oil level is not over this mark.


Replacing the rings is a pretty big job. But with only 500 hours on the engine, this is actually one of the least possible issues.


What I would suggest at this point is to first check the oil level.

Then I would remove the pulse line from the fuel pump and engine, and clean it out good.

Then I would monitor it for a while.

It is possible that the crankcase had gotten overfilled at one point, or if the unit was run on a slope, it could have gotten oil into the line. Once oil gets in there, it stays until you clean it out.

If it continues to get oil in it, then you may consider having a leak down test done on it. I definitely would not go through the expense of replacing the rings without having first done a leak down test.


Customer: replied 7 years ago.
HI, I replaced the cap on the packing with one from a blown engine and it no longer spits oil, I run it for 3 hours at full throttle and not a this WAS the problem....I cannot be satified with your answers since I solved the problem myself and you actually told me this could NOT be the problem, it seems the crankcase couldnt achieve a correct negative pressure with one of the balls missing, thats all I did and it no longer spits, so I have to assume that it was the problem..Thanks for your help