oil getting into the fuel?

[ahmebane]

More fuel woes. I went to fly today & did the usual preflight fuel draining. The wing drains were nice: clean, clear, bluish avgas. When I drained the gascolator, the most awful looking fuel I've ever seen came out - a dark yellowish color. I pulled about a cup of that gunk, then pulled about a cup where the color started looking more like light green, then finally good looking avgas came out.

The plane has not been flown for over a month (health issues). I took the fuel sample to my mechanic & he thought it seemed oily. The prevailing theory is that a seal has ruptured in the engine driven fuel pump & oil is seeping into the fuel system & draining down to the gascolator.

Anyone seen anything like this? I tried searching, but could not come up with a query that was useful.

TIA.

[Steve]

Holt:

I doubt that oil is draining into the gascolator via the mechanical fuel pump. The Lycoming pump has two rubber diaphragms. If either one has a leak, you will get a liquid (either oil or fuel) from the fuel pump drain line. You would need to have tears in both diaphragms in order to get either fuel in the crankcase or oil in fuel line. Plus, the fuel pressure in the pump is higher than the oil pressure (basically splash oiling from the accessory case, not oil gallery pressure), so even if you had tears in both diaphragms and a plugged drain line, I would expect fuel in the oil sump, not oil in a fuel line.

I guess anything is possible. The fuel pump is a relatively inexpensive part, but not all that easy to R&R with the engine mounted. One reason I replaced mine when I pulled my engine last summer:

Old fuel pump

New fuel pump

Let us know what you find out...

Steve

[smoss]

There was another thread on someone who had green fuel from the gascolator under similar circumstances. I think it turned out to be mold. If you search you should be able to find it.

[Rich]

A cup seems far more than the volume of the gascolator and the associated fuel lines. Did you check fuel from both tanks? I, too, have a hard time immediately buying into the fuel pump theory but don't have an alternative hypothesis.

Gasoline mixes quite readily with oil (witness two-stroke engines) as it does with things like kerosene. It sounds like there was not a clear delineation between yellow goop and nice blue stuff as there would be with water, so a hydrocarbon of some sort seems likely.

[ahmebane]

There was another thread on someone who had green fuel from the gascolator under similar circumstances. I think it turned out to be mold. If you search you should be able to find it.

Yeah, that was my thread, too! Its a real puzzler. No one in the shop has a good theory. The green fuel before appeared to be some sort of growth in the fuel filter. This time, the fuel came out a really ugly brownish yellow. Eventually was good. I did a runup & the engine ran just fine the entire time.

[ahmebane]

A cup seems far more than the volume of the gascolator and the associated fuel lines. Did you check fuel from both tanks? I, too, have a hard time immediately buying into the fuel pump theory but don't have an alternative hypothesis.

Gasoline mixes quite readily with oil (witness two-stroke engines) as it does with things like kerosene. It sounds like there was not a clear delineation between yellow goop and nice blue stuff as there would be with water, so a hydrocarbon of some sort seems likely.

The fuel from both tanks looked fine. We mixed a bit of used oil with some clean avgas & it looked very similar. And yeah, the fuel pump theory is a stretch, but at this point I dont know what else to do other than start taking things apart.

[ahmebane]

Perhaps since we saw mold or something in the gascolator before, it has regrown. Before the shop starts digging into the pump, which given 2 diaphragms would have to fail seems as an unlikely problem, I'll have them check the gascolator & fuel filter again. One thing the shop noted is that they usually see fuel filters being green & mine is black. Anyone know what that might be about? Too many mysteries for me....

[astaib]

Hi all,

Question: do you drain the gascolator everytime you fly? I drain both wings but never the gascolator, is it a mistake?
If you drain it often, can you tell me how you do it clean? Because the tool that I use to drain the wings and collect the avgas is not fitting for the gascolator.

Thanks.

Arnaud.

[danno2000]

If you drain it often, can you tell me how you do it clean? Because the tool that I use to drain the wings and collect the avgas is not fitting for the gascolator.

I drain the gascolator before every flight. I use the same type of poke-the-sump fuel tool I've used with other planes, and it works equally well on the wings and gascolator. Only thing I've seen is I have to keep it under the gascolator a few extra seconds as it seems to drip more than the wing sumps.

best,
dan

[astaib]

Is the gascolator as easy to access as the one of the wings on your plane?
Mine have a deflector that is blocking my little tool to drain.