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oil leak, maybe fuel pump housing?

M

Mike Buettgenbach

Active Member
I had just finished flying two legs, about 3.5 hours total.
I hadn't inspected the engine compartment for probably 20-25 hours, so I thought it was time to do so (just a good idea, I inspect every 25 hours or so)
What I found was a bit strange: there was a bit of oil on the oil sender hose (I have remote mounted the oil sender) originating just aft of the fuel pump. There was evidence of the oil dripping down on other things, but appeared to originate on that hose (the fire sleeve actually).
No leak or damage in the hose that I could find, and the hose has fire sleeve on it, also in good condition.
Very slight oil coating on the fuel pump. It did not appear to be coming from the pump mounting flange, but rather the crimped flange on the pump. . . . as best I could determine.

Again, the amount of oil was slight, but enough to cause a few drips over the previous 25 hours of flight.

I cleaned all surfaces, reassembled, and will evaluate over the next few hours of flight.

Anybody else seen similar leaks?

I expect I will install the new pump soon, but wanted to post the question for others, and see what evidence might be out there.

It is the original fuel pump, the aircraft has ~250 hrs.

Thx
 
Engine driven fuel pumps leaking oil are quite common. Unfortunately there is not a lot you can do to stop it. The pump has two diaphragms, one separates the pump internals from the engine oil, the other is part of the fuel pumping mechanism. The pump body consists of 3 castings with the two mentioned diaphragms sandwiched in between. Screws around the top and bottom hold the assembly together. Once oil seeps past the upper diaphragm, tightening the screws will not help because the diaphragm's flange between the castings is oily and will creep when the screws are torqued. This results in the holes in the membrane where the screws penetrate getting larger, increasing the leakage. I have had some success in disassembling the pump, cleaning all the oil off the castings and diaphragm and reassembling the pump. Be aware that this pump is a critical component in keeping the engine running and should not be taken apart unless you know what you are doing.

Martin Sutter
Building and flying RV's since 1988
EAA Technical Couselor
 
Yes, I just replaced my engine driven fuel pump for this very reason. The oil leak was determined to be from at least one of the small screws on the top side of the pump housing. It was not a big leak, just a drop or so around the top screw head after a short flight.

At first, I thought the leak was from something else, but could never find a different source. It was the fuel pump, the new pump has about three hours on it, and I have not detected any leak yet.
 
As I recall there is no sealant between the spacer block and either the pump or the engine block, so if the fasteners were under torqued it seems likely that seepage could occur around the spacer. Did you find them under torqued?
 
There should be a gasket between the pump and accessory case.

Martin Sutter
Building and flying RV's since 1988
EAA Technical Counselor
 
I think some posters are talking heritage Lycoming engines, not the Mighty Rotax.... ;)

There is no gasket as such on the Rotax pump to gearbox mount, just a thick spacer (non metallic).
 
I had one that leaked at the gasket between the fuel pump and the accessory case. When I would get done flying, the cowl pressure had blown the oil all over the bottom of the fuel pump (and everywhere else), so I always looked there and never could find the source.

One day, the light hit it just right wile I was looking for the leak and a little bitty line of oil was coming from the bottom of the gasket down to the oil sump gasket.
 
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