Onan fuel pump blowing oil out the vent

[Callen 64]

Is the oil too thin? I haven't changed it yet, just got it running. No oil coming out of the cc breather. Not over full.

First time I've ever seen a vent on the pulse side of one of these type pumps, there is usually a vent on the other side of the diaphram. It's an '88 or '89 520H. TIA Chester

[varosd 1,185]

not sure how engine oil is anywhere near the fuel line/pump. I mean... fuel tank>fuel line>fuel pump>fuel line>carb> engine. by chance, do you mean the air filter? oil soaking the element?

[TheReDStAnG 4]

Callen, you might want to take some pictures of what your seeing. I have never seen oil blowing out of a fuel pump vent and have 3 Onan's. The only problems I ever had with the with fuel pump other than dirty reed valves is a bad diaphram which allowed straight fuel to be sucked into the crankcase. It thinned out the oil, and blew out the crankcase breather on throttle down.

[1maidenfan 201]

Possibly the spring that is on top of the reed valve, might be broke or missing and allowing crankcase psi to blow oil past the reed valve and into the breather hose and then out the fuel pump vent.

Or you have an oil leak some where and it is dripping or running down the tube and just looks like it is coming out the vent.

:text-welcomeconfetti:

[Callen 64]

Oil runs straight down the shroud from the fuel pump. I just took it apart and replaced the pulse line because I thought that is where it was coming from. can't get a good pic of it. It will leave a puddle if i let it set and idle for a few minutes.

[varosd 1,185]

_{how is it running?}

_{does it have full power?}

_{does it happen even at idle vs full throttle or under load such as when the PTO in engaged?}

_{Is this a new 520 to you? meaning was it not running prior?}

[Callen 64]

I bought it with issues. Cleaning the carb fixed that problem. Then I got a nostart condition. Cleaning the pin connecter fixed that. Now the oil leak. I wonder if the crank case breather is working. The RPM and load doesn't seem to make any difference on the leak.

The vent in the pump still bothers me because it can draw dirt through the pulse line right into the crank case.

It does run good, just a little black smoke on throttle up.

[varosd 1,185]

could be the breather, there is a reed valve, diaphagm,and "pack" material that is supposed to be changed out time to time. the Onan manualhas more info and downloable under Files. Take pictures as you pull stuff apart, labeled ziplock bags etc. I had a no start issue shortly I got my 520 and got know the machine quite well!

[Callen 64]

Interesting....My breather looks like one from a 224. I'll have to look deeper when I get a chance. Thanks for the help, guys.

[Herbl 10]

Just wondering if you call one of the top spouts a vent, one should have a fuel line on it and the other top spout should have a plug over it, it should not be open. At least that is what I have on the 3 of my 520H's...

Herb

[Callen 64]

it's a 1/16 hole in the back of the pump, toward the shroud.

This engine was replaced at 700 hrs, I'll have to pull a head cover and count the head bolts, The breather looks to be a 224, no breather in a tin cover, the breather sets right in the block.