Hi Larry, Two points. As it was explained to me, the diaphragm in the AC pump is a double one. If the top layer fails, gasoline exits the fuel pump via a hole drilled in the side of the pump, and this symptom is NOT an invitation to apply JB Weld and keep flying. For fuel to get into the oil, the bottom layer must also fail.
If you replace the pump, I don't know why you would need to change the oil. You should be able to tell if the lower diaphragm is intact or not. In WWII, most aircraft had an "oil dilution system" for use when the weather was cold. It mixed gasoline in the oil to lower the viscosity and as the engine warmed up the oil quickly got rid of the gasoline and viscosity returned to "normal". I see no reason why your situation would differ if you did have a bit of gas in your oil since it's still winter most places. Regards, WRB -- On Feb 2, 2010, at 16:07, Larry Snyder wrote: > I had sent out a note a week or so ago about a smell of fuel in the > plane whenever I was throttled back and descending. Today I taxied out > with intention of flying around a bit and experimenting with throttle > settings, attitudes, etc., to get more empirical data. I never made it > to the runway! The smell of fuel was overpowering. I taxied to the FBO > and when I looked at the plane I could see streaks of oil/fuel down > both sides of the cowl. The plane was clean when I left the hangar, so > obviously fuel was washing oil off all sorts of parts and creating the > streaks down the side. The mechanic stood in front of the plane as I > cranked it over, and the fuel pump was squirting fuel out the front. > The prop was then distributing the fuel all over the engine. > > I am assuming that in recent flights the leak was much less obvious, > and the air flow through the cabin was altered enough during descent > to let some of the smell of the leaking fuel get in. In normal flight, > there was no smell. Today it appeared that some gas had leaked into > the oil, but not much. The level did not appear higher, and the oil > was still viscous, but I think it was a bit thinner. > > We will replace and pump and change the oil and all should be well. Of > course, the pumps are insanely expensive. But then, it is an airplane. > > Larry > N99340
