Small Onan Oil Leak...Ideas?

[ropari]

I have a garden tractor with a new 20 HP Onan Performer. I am thinking about the possibility of selling it, but want it to be tip-top before doing so. My problem is a small several drop oil leak after using it. The dealer says I am nuts, but it really does appear to be coming from the plastic fuel pump. It runs down the outside of the engine cover where the vac' line goes through to attach to the pump. I see none on the inside of that cover. There is nothing slashed anywhere else like it is being thrown and none on the inside of the hood which fits down right by the pump. There are absolutely no other leaks anywhere else on the outfit. Now I will also tell you the tractor seems to need a lot of choke to run well even when warm, but works well and has a lot of power. I plan on changing the break-in oil and filter today , and would also like to see if this leak can be fixed while it is raining outside thereby keeping me inside. The dealer has me convinced I am nuts, but thought I would run this by you all, before hauling it all the way there and paying $60/hour. I had considered buying a new pump, about $50, but the dealer says no way can that be the problem as oil in the vac' line would keep the tractor from being able to run.

Thanks for any advice.

[ropari]

"Splashed" not "Slashed". Also, the dealer had told me to just use it and not to worry as it was no big deal. However, even should I keep it I hate any type of leaks on my equipment as I keep my stuff stored inside my garage.

[ropari]

A short while back I posted this question concerning a small oil leak from a new Onan engine. I received no replies as to what might be causing it. Since it was such a headache to me, I thought I'd post what I found, just in case anyone runs into this sometime.

The leak appeared to come from the vacuum operated fuel pump, but I was told by a couple of dealers that this could not be. After much time looking for leaks elsewhere with absolutely no luck, I sat over the engine with a flashlight and let it run. In daylight this could not be detected, but from the pin sized breather hole in the back of the pump, "tiny" little specks of oil were popping out as the engine ran, eventually accumulating enough to run down the engine cover. Since this had not happened when I first bought it, and it still has only about 5-7 hours on it, I had some thinking to do.

Recently I had changed the break in oil to a 10-30 synthetic. Reading the owners manual I saw it suggested a straight 30 weight for summer use. I changed to a 30 weight non synthetic oil, noting that the warm synthetic oil drained out like water. After changing the oil I let the engine run for an extended time, no more leakage.

One of my other tractors just showed a touch of dampness from the oil cooler area, which it had never shown before. I had just recently put the same synthetic oil into it, so I am going to check that out, too.

This may not be news to you mechanics but hopefully this may be useful to some others at some point in time, who like me, learn as we go. I know I saved a bunch by not having to take this into a shop and being charged $60 per hour.




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[Argee]

So what have you concluded to be the cause of the leak?? The 10-30 synthetic maybe to thin?? That's an interesting problem.

[ropari]

Randy...basically, yes. I called a mechanic yesterday and told him about this. Since he had not seen the engine he had assumed a hydraulic leak somewhere, being splashed onto the engine cover by the air from the fan. When we discussed the results, he was not surprised. The vacuum line comes out of the crankcase, so with the thinner oil it appears there was enough pressure to send a bit up the vacuum line as the tractor was working. The diaphram pumping must have caused the small amount of oil to be pushed out the breather hole on the pump. Best I can come up with, not being a mechanic, but thinking and discussing with one. Not sure if the synthetic had anything to do with it, or if it was just the viscosity. But, I have drained warm dino-oil before and never noticed it being so thin. I am not knocking synthetic and will still use it in my wife's car, but I may go back to dino for all my lawn/garden equipment.

[Jim_WV]

Rop, not being a mechanic I did'nt reply to your orginal post as I had no clue what the problem could be, but after reading what you found out here, I have to say thank you for posting it. Perhaps it might save someone the same headache down the road. I began using 10w30 synthetic after I accumulated 25 hours on my Briggs 20HP and I use it year round, so far so good. I am wondering if you went to syn. too early ?. A lot of lawn/garden tractor owners have said they always wait to go to syn after at least 25 hours or more are on the engine, but to know whether this is a factor for leaks or not is still up in the air.

[chrpmaster]

Jim

I had always heard that you wait to put synthetic oil in a new engine to allow the rings ect to get set in properly which prevents oil leaks and burning oil later.

I know on my old Case tractor I have an oil bath air cleaner that I cannot put too light an oil in or the suction will pull it into the carb/engine and make it run lousy. Sounds like thats what was happening to ropari too.

I guess that does prove the point that those owners manuals need to be read after all! :fing32:

Andy

[bontai Joe]

Thanks for posting what you discovered! I had no idea why you were suffering from an oil leak, and would never have guessed that the synthetic was thin enough to come out. Another of life's mysteries solved.

[Mickey]

IMO using "thick" oil is not the solution to a leak in FP diaphram. I'm wondering why if this is a new engine it isn't being taken care of via the warrantee? The "vac" comes from the changing crankcase pressure as pistons move up/dn the cyl. It is possible to find small amounts of oil in the line to the pump, especially true if there is an opening at the end of the line for the air to flow in and out of. Small opening for sure but open none the less. This would not be the case if the diaphram didn't leak and no place for the air/oil to go.

[ropari]

Mickey...I am just trying to learn. Could you explain your last sentence? Not quite sure I understand what you were trying to say. Just to be sure on my end, there is a factory pinhole for breathing in the back of the FP.

As for the engine I have no warranty. It was purchased in quanity from someone closing shop. A dealer bought them and this one was put into a tractor I purchased from him. I purchased it out of state anyway, so would not want to haul it back there even if he would work on it. But, bottom line, I have no factory warranty, :o( , although I don't think this is any real problem. It was more of a nuisance having a drip of oil every time I used it.

Thanks,
Bob

[Mickey]

It been a long time since I looked at one of these and really don't recall if there is one or two diaphrams. I think you'll find the pinhole you see is so air is not trapped behind the diaphram as this would hinder the movement of same. I think what you want is for the varying crankcase pressure to pulsate the diaphram and pump gas. You don't want the FP to function as a breather for the engine. Since pressure is provided by the lower end I would expect oil to be slung around and possibly find it way up ino the tube for the FP. If there is an open passage at the end, the pump itself, I wouldn't be too surprised to find oil present. Not much but some.

On the otherhand I could be all wet.

[ropari]

Thanks Mickey

[simple_john]

:bump9:
Bump


Bob, did you ever get this resolved??