Fuel Smell

[207WF]

I have been smelling fuel for a while in flight. At first, it seemed the like the carburators, which were leaking, but Roger Lee fixed that. Maybe the smell was a residual and would go away. But it did not. The rubber hoses from the wing to the cowl area were recently replaced, and I was afraid they might be leaking. On today's flight I stuffed some thin rags down the channel that runs between the wing and the cowl along the windscreen. After a 2 hour flight they came out dry and did not smell that much of fuel, and there is no indication at the lower end of those hoses in the cowling that they might have been leaking. There is a slight smell near the sight gages, which were also recently replaced, but no signs of leaking there. I checked the fuel shutoff and screen behind the instrument panel; no joy. The smell is strong at engine start and continues during flight, and it seems to me to mainly come in through the window air vent. I am running out of ideas. Anyone have some? WF

[Roger Lee]

Hi Wayne,

 

Give me a call at home.

[chanik]

Possibly unrelated, but I was chasing fuel smells for awhile myself. I sleuthed it down to whenever the wings sloshed with full tanks, either when taxiing over bumps or flying in turbulence. Turns out the O-rings would leak fuel which runs back to the flap/wing gap and then runs inboard and into the rear compartment. I could see it from the streak stains after I landed. Seems there is plenty of cross ventilation back to front and it doesn't take much to smell fuel. I replaced my O-rings with Viton so they never wear out and that mostly got rid of the problem but viton is not quite as rubbery so still had some small leaking especially when the plane wasn't parked level and with full-ish tanks.

 

In order to get a great seal, I went hunting for fuel-proof grease which is sort of a tricky requirement if you think about it. It almost doesn't exist, but there is this odd stuff from DuPont called Krytox. It is sort of wonder-grease and priced like it too (~$90 for 2oz tube). Zero outgassing, dissolves in nothing, stable on high speed bearings at 300C or -200C in liquid oxygen. They use in with scuba systems, microscopes/telescopes, spacecraft, etc. Anyway, a thin bead of that on the inner and outer o-ring was adequate to seal the tank caps very well. 240AC has about the viscosity of vaseline so that's what I got; most Krytox variants are thinner. I got some on my fingers and well, I just had to put up with greasy fingers for a couple days.