What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Oil from Fuel Pump Overflow

Kyle Boatright

Well Known Member
For some time now, I've been parking the airplane and coming back a few days later to find a spot of oil under the aft edge of the cowl. We're talking a half ounce of oil, maybe less - a very small amount. During flight, there are/were no apparent leaks (no oil on the belly) and I haven't had to add oil to the airplane. I've looked for the "after shutdown" leak a couple of times with the cowl off, but didn't identify the source until today.

It looks like the oil is coming out of the overflow line for the mechanical fuel pump. Is there any explanation other than a faulty diaphragm in the fuel pump?
 
The verdict is as good as your diagnosis - if it's really oil coming out of the fuel pump overflow line, then it's really your fuel pump diaphragm.
 
Kyle, out of curiosity, how old is that fuel pump?

There is a lot of evidence in various threads and posts here that they should be preemptively changed every 5-8 years. Dan H. posted detailed observations on the diaphragm breakdown in a startlingly short time.
 
Kyle, out of curiosity, how old is that fuel pump?

There is a lot of evidence in various threads and posts here that they should be preemptively changed every 5-8 years. Dan H. posted detailed observations on the diaphragm breakdown in a startlingly short time.

This one is just over 4 years old. My first one lasted about 15 years.
 
.....

Is there any explanation other than a faulty diaphragm in the fuel pump?

Yes. At certain flight regimes the oil from breather swirls corkscrew. Couple drops could be trapped in the camloc by the drain. Could even leave a trace after your next flight. The trace would start from the pump drain.
 
Yes. At certain flight regimes the oil from breather swirls corkscrew. Couple drops could be trapped in the camloc by the drain. Could even leave a trace after your next flight. The trace would start from the pump drain.

I used a clear line for the vent, makes it obvious, can see the oil in the line.

I have been in this same boat, time to change the pump.
 
Back
Top