The International Cessna 170 Association

I am having gas coming from the area of the gas caps. The gaskets are tight. I am suspecting the gas is coming out of the vents in the caps. Both caps are vented, plus the large forward facing vent on top of the cabin. I was wondering if the pressure from the forward facing went was creating too much pressure in the tank for the vents to hold back???? O-360 engine.
Sound familiar, anyone have the cure.

A friend said he had a similar problem on his 175 and used a non vented cap on the right tank.

Thanks gary

The caps when serviceable will hold back pressure created in the system. One vented cap or two. The AD requires one vented cap. But two also meets the AD. You could get a non vented cap and test it on one side or if only one side is leaking, switch caps and see if the leak follows.

I suspect your leaking fuel is coming from either the cap gasket or more likely the gaskets that hold the "moat" to the tank and the top wing skin.

Check the serviceability of the little red flapper valve in the underside of the fuel cap. If it is missing or leaking fuel will vent out of the cap .these red rubber valves get old and fall apart which the allows fuel to flow out . The big problem is you can't buy these separately it's a new cap .

I looked at the cap vent, appeared fine, but I may have to look closer. I have some other old caps. Probly stick a non vented cap up there and see what happens.I am hoping to long range fuel tanks soon, either with 175 tanks or 175 wings and tanks. Still looking for the best path for approval and trying to gather supportive documentation
Thanks Gary

shortfielder wrote:I am having gas coming from the area of the gas caps. The gaskets are tight. I am suspecting the gas is coming out of the vents in the caps. Both caps are vented, plus the large forward facing vent on top of the cabin. I was wondering if the pressure from the forward facing went was creating too much pressure in the tank for the vents to hold back???? O-360 engine.
Sound familiar, anyone have the cure.

A friend said he had a similar problem on his 175 and used a non vented cap on the right tank.

Thanks gary

I had this same symptom, incidentally with the same motor. It turned out to be the rubber vent valve on the inside of the cap. The little rubber stem was starting to stretch and break, which allowed the valve to stay unseated while gas would siphon out of a full tank. Had to buy a new cap which I believe was only $26 so I replaced both sides.

I was fortunate enough to have caught it before the darn thing fell off into the tank. I suspect it would be the perfect thing to block the fuel line on that side.
Chris

Replace the cap

I doubt that the small piece of rubber on the fuelcap valve would interupt the fuel outflow from the tank since there is, or should be, a finger strainer on the fuel line.

Where is the best place to buy new fuel caps?
Thanks Gary

Cessna distributors. Try www.cessnaparts.com which is Hill Aircraft. They will give you a 10% discount as a TIC170 Member.

Thankyou Sir
Gary

I know this is an old thread but I was wondering if anyone has had any luck sourcing the little red flapper as the cost of the cap has gone up 300% since this was written?

adedominicis1987 wrote:I know this is an old thread but I was wondering if anyone has had any luck sourcing the little red flapper as the cost of the cap has gone up 300% since this was written?

It looks like Jim Collins was successful locating the umbrella valves here. I think this is the valve he bought. I see they have a "free samples" tab. Might be worth trying.

Yes, "MiniValve part # UM145.003-544.01 made from FVMQ (Fluorosilicone)" is an exact replacement. I have been using these and they are working just fine. I had to get these as a sample because their minimum order was too large and if I remember right, one order could have re-equipped all of our 170's with some left over.

LOL. thanks for the info. So just to be clear, you didn't put in a huge order?

Just a quick update......I was able to order some valves through minivalve. Because the FVMQ is a special order, I would have been required to order 100 at $3.80 a piece. They put the order in as a sample as they had a few on the shelf and just charged $45 shipping as they are coming from the Netherlands. Because I am impatient, I continued to search for an alternative and discovered Holly Carburetor part #26-41 accelerator pump check valve is an exact match. It can be purchased as a 2 pack from advanced auto for $12.99. I hope this helps someone in the future