The International Cessna^® 170 Association

As with any request I am expecting to hear all sides so here goes...Way back when I was a young pup, I was taught to switch the fuel selctor to "OFF" when through flying. The rationale was that if "something" where to "let loose" then all the fuel would be on the floor of the hangar. Recently I am seeing blue residue (AV100LL) directly underneath the value and the leak rate is perhaps a few drops per month if that. My mechanic suggested to "leave the valve on both tanks." The rationale being that if the valve seat, gaskets whatever were wearing then each time the valve is turned creates additional wear. This seems logical as well. NOW I am noticing a larger quantity of fuel seepage coming out of the carburetor. I always top tanks after each flight whcih probably results in a "pressure head" going directly to the carb.

QUESTION: What is the prefered method, if any?

QUESTION: What is the prefered method, if any?[/quote]

The prefered method is getting the leaks fixed. "O" rings in the fuel selector, and a new float valve in the carb.

Getting the problem fixed is always the best but sometimes we get caught low on funds. In that case I would go back to turning the fuel off until I could get things fixed. I have seen in the last year, two different airplanes dump 40+ gallons of fuel onto the hanger floor by not turning off the fuel. The problem in both airplanes was the float sticking "sometimes" in the Carb. One guy thought someone was stealing fuel from him. Sometimes it would leak and others it would not. When it did by the time he showed up to fly again the wet area would be dry. Sounds like you need both a rebuild on your selector valve and a needle valve in the carb. Good Luck

Airplanes, motorcycles, boats, etc.,...the reason a fuel ON/OFF valve exists is the same. When not operating the machine, turn it off. (In fact, for long periods of storage, you should turn it off and run it until it dies.)

Thank you all for your professional responses. I have once again elected to turn off the fuel selector after each flight and run the engine dry. Fuel seepage from carb has ceased. Also, not blue stains under the fuselage near valve.
At next annual carb and fuel valve will be re-worked.

Remember that the fuel can still cross feed from one side to the other when in the off position. So if you are parked on an angled beach clam digging or you are at the fuel pumps trying to get every drop in you can, the only way to keep it from crossfeeding is in the right or left position.

Kelly

You know, Kelly, ...that is the darndest thing! So many tell me that the tanks will cross-flow in the off position, but I've deliberately run one tank virtually dry with the other full, left it in the hangar in the off position for two days, and there is no cross-flow occurance on my airplane. (1953 B-model, SN-25713). Go figure.

I think the only way a crossfeed can happen with the selector turned off is if one tank is so full it bleeds over to the other through the vent lines.