Fuel "Leak" Mystery

[Steve Brown]

Hi all,

A while back when I was filling the right wing tank, significant fuel leaked out between the wing and the fuselage. It stopped very quickly and has never happened again. As far as I could tell, it wasn't running back from the vent.

It seemed to clearly be a vent type issue since the tanks holds full fuel, and if its been hot, fuel will gush out when I open the cap. As expected.

I inspected the vent line, feed through/s, elbows, and found nothing. Everything was tight, no kinks, nothing.

I pushed some tubing over the vent and blew into it with the filler cap on. It felt sealed, at least as hard as I can blow. That should be hard enough. Since the fuel only has to rise about 2 feet it shouldn't take much pressure.

When I pulled the cap and blew on the hose I could hear air venting into the tank.

So, the vent is neither clogged nor significantly leaky.

I've put about 30 Hobbs hours on the plane since the "leak" incident. It's never repeated.

Everything seems ok, but I haven't got an explanation for the fuel coming out between the wing and fuselage. Its kind of nagging at me.

Anyone had a similar problem or know of a different test I should conduct?

[WilburD2]

Steve, my suggestion would be to drain the tank fully and let it sit for a few hours. Then with you watching, have a helper refuel it again. Could be something simple like a dry seal that expanded when the fuel hit it.

[sprucemoose]

...when you were fueling, is it possible that you overflowed the cap? The fuel tends to run aft to the tank skin/ aft wing skin joint, then flow inboard along the joint until it runs down into the wing/ fuse gap.

Possibly that's what happened?

[Steve Brown]

Thanks Jeff & Bill.

"Could be something simple like a dry seal that expanded when the fuel hit it."

Bill,
A bit of information that I didn't think was relevant was that the tank had been sitting dry in hot weather for 4 days. I ran it dry on my last flight to prepare for replacing the quick drain.

After the repair I fueled the wing to be sure my valve wasn't leaking. That's when the leak occurred, and it was relatively early in the fill process. Well before the wing was full.

It all makes sense now. Also, makes me think that letting the airplane sit with empty tanks is probably not a good idea.

Yesterday before I posted this problem my wife was the one who remembered that the leak was the first fill after the repair. She thought it was important, but I told her it was irrelevant information.

I guess I'm having humble pie for breakfast.

[swisseagle]

Hello Steve

Did you use the kork-rubber seal on the tankacessplate and the rubberseal on the fuelsender?

I know there was an issue about the fuelsender-rubberseal when you where using mogas(autofuel), they swell and start to leak.

If you are using proseal only to glue/seal the tankaccessplate and fuelsender, there should be no leak ... also when they sit around when dry.

Hope it helps,

regads, Dominik