Leaking wing tank or something else?

[tj_od]

I've got a mystery I'm trying to sort out. I think I've got a leak in my left tank, or maybe something wrong with the fuel selector. Initially, I was ok with not using the left tank and running off the other two. Maybe tackling it at annual. However, some other oddities have happened and I've resolved to have it looked at sooner. Would appreciate any insight/suggestions prior to bringing it in. Here are the "facts" as I understand them.

I've got two wing tanks that feed to a 3 way valve in the panel (it looks to be a Weatherhead p/n 6749). I'll attempt to attach pictures but just in case, the selector on the panel is labeled up: wing tanks off, right: right, left you guessed it) left and, down: both.

The left tank cap is super tight, the right tank is loose(r), I did cut new seals to tighten it up but it's still not as snug as the left tank (which almost takes two hands to open).

The spot I park in lists slightly downhill to the "leaking" tank. The leaking tank was leaking even when it wasn't full, full. It seems to hold some in the bottom of the tank without leaking. I poured in enough fuel to be able to sump from the check valve and it didn't show signs of leaking anywhere.

I've opened the fairings inside and out to look for obvious leaks or other issues and saw nothing.

Now the anecdotal info:

I filled all tanks one evening in preparation for a morning flight. Selector valve was vertical towards "wing tanks off." I arrived in the morning to a gas smell, and observed fuel weeping out of the back of the wing. I hurriedly drained the remaining fuel in the left tank. This is where I resolved to just run off the main and right.

Flew a bunch of times. Didn't really use the right tank, but it seemed somewhat lower. I started to wonder if I had a slight leak in that one too. Went out one day to do some steep turns, etc. (running exclusively off the main) and came back to find the right tank empty (at least to the measure of my fuel dipping stick) and the left tank with some fuel in it.

I did find that the selector valve may have been angled a bit toward the right tank selection. You can't really feel when it clicks into a setting, but without a headset, parked on the ground there's an audible click as it moves from one setting to the other. I clicked it in place (wing tanks off) and now the right tank seems to be holding its level.


Here's what I'm wondering:

1. Is there any possibility the tanks are cross connected someplace else other than the main lines... is there a shared vent tube or something? I can't find any detailed drawings with fuel systems in the forum materials and I suspect mine is modified anyway (and maybe not to spec in accordance with STC # SA1-210 for which I don't have the drawings related to fuel).

2. If there is an issue with the fuel selector why didn't it overfill the main instead of flowing into the other wing?

a. if I had the right tank selected but the valve not all the way open, wouldn't it have dribbled into the main
b. is there a way for the selector valve to fail internally in such a way that it would permit cross flow but not into the main
c. is anyone familiar with the internal workings of a 3way valve like this (Aircraft spruce boasts the Weatherhead part has a "Derlin-spool design" but I'm having a hard time finding an exploded diagram of how it functions).

3. Just in case the tank is a leaker, are there any Alaska Taylorcrafters with an extra wing tank or two that they'd be willing to part with? If/when I have to tear into the wing or recover, I'm also toying with adding extra tanks...

Thanks for any help,

TJ

[astjp2]

leak at either the tank or plumbing, have a knowledgeable mechanic look at it...if the tank is leaking you will either fly empty on that tank or probably will have to cut fabric to get the tank out. Good luck tim

Ok, what engine do you have? if you have the 85, they required a vent in the wing root that connects both tanks, if 65, then no...

[tj_od]

It's an 85. Where does the vent typically cross over? I've got a skylight, and, didn't see anything (other than the fuel lines exiting the tank) when I took off the aluminum covers on the interior of the wing root. Thanks!

[tj_od]

I should add that it's going in next Monday for a troubleshoot and hopeful fix. I've posted here in hopes that I can help point them (quickly) in the right direction.

[3Dreaming]

The vent shout cross at the upper front cross tube behind the windshield. The other thought I had is the valve is allowing the fuel to cross feed. This would also match your described behavior.

[tj_od]

Update. Borescope revealed some separations on the tank seams on the forward end of the tank (explains why it holds some fuel when parked). Jury is out on the crossfeed, best bet is the valve was not fully clicked in place on main and slightly open to the right. Still not sure why it wouldn’t have overflowed the main tank, but there’s been no further crossflow. Anyone sitting on some wing tanks they’d be willing to let go?