Hi, my fuel tank vent (underside left wing - p/n 0716125-2 located inside tank) leaks excessively. Curious if replacement is best option or is it designed for simple rebuild with new o-rings? Thx. -Ray

Does it leak only when the tank is full? Is it parked on level ground? Is the plane parked in the sunshine, heating up the fuel so that it expands?

If it's leaking when the tank is half full, there's probably a problem. It's quite common to have fuel coming out of the vent just after filling the tanks if the plane is out in the sun, or if it is not level.

I *think* you can address that by putting the fuel selector to OFF. I don't know if the interconnect between the right and left tanks will continue to feed the tank that is overflowing (not really leaking).

Good thoughts here and that is correct. You can stop inter tank fuel transfer through the fuel selector while in OFF, RIGHT or LEFT.

Here is a photo of a 182 fuel valve opened up. The body is upside down while on the bench.




The vent interconnect will crossfeed fuel up to a certain point. Certainly, with partial tanks and parked on an unlevel spot, the fuel has the potential to transfer between tanks.

The fuel vent is nothing more than a flapper valve, hinged at the top. Even so, it has a pinhole to always allow some venting. To access it, you need to pull the outboard fuel cap on the left wing. As Tom said, leaking fuel is quite common.

McFarlane Aviation makes and sells a fuel vent line for the 182 that has a "trap" in it that helps stop some of the fuel venting problems. I have one installed and it works quite well but is not a 100% solution.
https://www.mcfarlaneaviation.com/produ ... ent-lines/

One more thought to the OP. You don't mention whether this leak is on the ground or in flight. If the vent line is not properly adjusted in relation to the left wing strut, you could be pressurizing the fuel tanks and causing excessive venting. The fuel vent needs to be adjusted vertically to stick down below the wing strut 0.19". Yes, it's that precise.

+1 on the McFarland vent line. I put one in my 182M a couple of months ago when changing the fuel bladders. Seems a shame to pay that much money for a bent piece of aluminum tubing but it works.

Dave

Ray,

Just NIL...

Item 10 in the attached drawing is what you refer to as "leaking"? Is the fuel coming out of the wing through the vent behind the pilot side strut or flowing across to the other tank or coming out the bottom of the wing? All 3 are possible.

If fuel is just flowing to the other tank simply shut off the fuel valve when on the ground etc as suggested above - simply a "feature" of the 182 fuel vent system.

If fuel is coming out the vent behind the strut when parked on level ground several possibilities, none simple to fix. E.G., the tank cap(s) have an issue.

If fuel is coming out the bottom of the wing you likely have a bad nipple on the bladder where the vent line enters - a problem very difficult to see and 1.5 AMU to fix.

If #1 or #2, the McFarlane vent change will likely solve your problems unless it is the caps.

Phil S is dead on re the very precise adjustment needed on the vent behind the strut. If out of place the tanks will cross flow or pressurize in flight or other bad things.

I rarely if ever go topped tanks simply because it invites the vent to send 100LL to bad places.

RAS

Many thanks to all...

Leaking is from the vent tube under the left wing in the hangar after top off. I realize in this scenario seeping is normal through the safety portal but I'm seeing 3-4 gal over a few days, which I think is abnormal.

The McFarland vent tube is interesting but my vent tank boss is tight up against the upper wing skin making me wonder how much headroom there is for the trap. I'll check tomorrow.

No matter - I removed the valve and it doesn't appear re-buildable, no after market options for new appear to exist, and after 50 years I figured what the heck so I bought a new check valve from CE$$NA. WOWEE!

Thanks again.

Ray

Just as a side note.... Don't open the fuel selector up unless you are very skilled at making tools to reassemble it or are going to replace it. What that picture doesn't show well is the nylon cups to the fuel lines have springs that push the cups toward the center of the valve (notice the cups are almost completely visible in the picture). I ended up making tools to hold the cups in place until the center selector was installed, then remove the tools.. It seems like the clearance on the sides of the center selector was tight enough you couldn't get a shim in place to hold them.
Just a warning....