Oil Leak Through Fuel Pump?

Doug Rohrer · #1 08-09-2020, 01:52 PM

I have a new RV-9A with a rebuilt O-320 carbureted engine. I have had a persistent oil leak on the rear of the engine but could not pinpoint the source. The most noticeable oil collection seems to be around and under the new Tempest fuel pump. Oil builds up around the pump OD and on the bolt heads going up from the bottom. Everything is dry above the pump. I put a cloth "diaper" around the fuel pump held on with zip ties for a temporary test. I flew an hour today and looked up from the belly. Everything looked dry and virtually no oil on the belly. This seems to confirm oil is somehow getting through the fuel pump from the inside out. I have snugged up the screws clamping the pump together, but still see oil. Is this a common problem? Any solutions other than changing fuel pumps?

Robin8er · #2 08-09-2020, 02:01 PM

It could be the gasket, it's pretty easy to replace. The safety wire is probably the hardest part.

Janekom · #3 08-09-2020, 02:04 PM

It seems like that new pump's diaphram, but I find it strange. What I do know is that it is a very common place to see oil drops hanging when they actually come from another source.

John Tierney · #4 08-09-2020, 02:28 PM

I had similar drips under the fuel pump, and my big leak was coming from the PMAG area just above the pump. The MAG gasket was not meeting up perfectly between the case and PMAG, and the nuts on the clamps (tough to get a socket on) had loosened.

Vlad · #5 08-09-2020, 02:54 PM

Gaskets are likely leaking. Either pump seal or mags. Tighten bolts and nuts and keep testing.

Malndi · #6 08-09-2020, 04:29 PM

I had a similar issue with oil appearing on the bottom of the fuel pump, with little sign of oil anywhere else. So I was initially convinced it was leaking from the fuel pump. After lengthy investigation the source turned out to be a very slight weep from around the oil temp sensor. A new crush washer fixed it.

Doug Rohrer · #7 08-09-2020, 09:01 PM

I will check torque on the fuel pump and PMAG bolts/clamps. Maybe get a mirror up in there to look closer for the source. It sure is tight next to the firewall.

gasman · #8 08-09-2020, 10:55 PM

The case is drilled through for the fuel pump bolts. You should use thread sealer on the last few threads that penetrate the case .

n18pf · #9 08-10-2020, 09:31 AM

Quote:

Originally Posted by gasman

You should use thread sealer on the last few threads that penetrate the case .

A friend with a Long EZ just had this exact issue. He had no sealant on the bolt threads. He sealed them and his oil leak is gone. The gasket was fine, it was the bolts that were leaking.

krw5927 · #10 08-10-2020, 11:25 AM

My Tempest pump did the same - a drop of oil forming on one or more screw heads on the bottom of the pump after every flight. After a thorough investigation, oil was not getting past the gasket nor the two (un-sealed) mounting bolts to the accessory case.

I bought a Lycoming branded pump and the problem is gone.