Fuel leaks out of vent!

[cranland]

I had leaking around my cap and was suggested to purchase gaskets from Mercedes. They work great. Still having a problem. The other day I fueled my 6 (about 1" from the top) THen flew back to my airport, forward slipped prior to landing. When I stopped and turned around fuel was coming out of the tank vent tube on the right wing. THe same wing that was leaking before. Any Idea what would cause this? I also noticed the see through vent line from the header tank back to that wing was full of fuel, is this how it should be? Frustrated because my white wing is blue streaked from the 100LL. Also any suggestion how to remove that? Tried using 100 on a rag, wax, even rubbing compound.
THanks for any info causing this fuel discharge.
Peter

[GoingHawgWyld]

I wonder if the slipping caused fuel to overfill the lower tank making the fuel leak? I would not think it could happen that fast but if you were not flying level maybe it could cause it to fill from the other tank? Hmmmm

[Dorsal]

My tanks will definitely leak through the vent tube if I slip with full (or near full) fuel. Actually to be fair I only assume it is through the vent tube but that makes sense to me given it only buys you a few inches.

[Dave S]

Peter,

A couple ideas.....

I have never filled my fuel tanks to within 1" of the top......I stop when there is 13 gallons on board which leaves about twice that distance to the top of the fuel level.

Fuel transfer from one side to another won't happen real quick due to the size of the tubing connecting the tanks and header. However, I have found out:o that it is entirely possible to transfer a significant amount of fuel from one side to the other if the plane is not level when parked or if flown with one wing slightly low....it takes a surprisingly small amount of other than level to do this. With really full tanks, probably wouldn't take much out of level at all.

I don't know that fuel transfer would occur any faster with a slip, but the fuel, particularly with a really full tank, could potentially slosh over to the outboard end where the fuel cap is with a good slip and possibly leak out the cap. I know you can't fold the wings with anywhere near a full tank and expect the fuel to stay in the tank with the tail down. With a slip...the spill would have to occur on the down wing.

I don't know if it was my somewhat active imagination; but, early on in testing, I noticed that my fuel cap pitots were not pointing quite the same direction (straight ahead); and, after bending them to be perfectly straight ahead found that I had lessened the fuel transfer issue.....either that or I finally figured out how to fly level!:o.

I'd also take a look at the fuel cap pitots to be sure both are clear and open full length. Although a Kitfox takes off and lands slow enough the bugs should have half a chance to get out of our way, I find that they don't always do that. A partially plugged pitot on one side may cause an uneven over fuel pressure when flying between the tanks.

Regarding cleaning up the 100LL stains, people may have some ideas if you can identify what kind of paint you have (example....polytone or aerothane) Not all paints can tolerate all cleaning solvents.

Sincerely,

Dave S
KF7 Trigear Flying
912ULS Warp Drive
St Paul MN

[cap01]

i think dave is on to something with the vent tubes . i had a problem not with transfering but feeding from one tank only. one tank would run dry to the point of turning the header tank low level lite with the other tank still mostly full . i fought that for some time until i removed some of the bend to the vent tubes on the tank caps , pretty much a 90 degree bind is what i ended up with . that was almost a year ago and havent had a lite come on since , except after ived drained the header and gotten air in it . while i was having the problem with the lite , i installed a shut off valve in the gas line from the left tank for troubleshooting that problem . the valve has worked out so well that ive left it installed . rarely do i completely fill the tanks , usually 15-18 gallons total and fly with the valve closed using the left tank as a reserve . the valve also prevents transfer and overflow of the tanks when parked on an uneven surface .

[cranland]

Thanks for the tips guys. Sounds like I'm just filling the tanks too much. My 6 is trigear and I have been filling it within 1" from the top.:confused:

[Dorsal]

I regularly fill mine right to the rim, I just try not to slip much when it is full.

[BigJohn]

I found that if I fill both tanks completly full that i could get some overflow through one of the vent tubes early in the flight especially in slipping right away or steep bank turns for an extended time, also I would get cross feeding throught the vent line and header tank between tanks if I parked on a slope, So I put in individual shut off valves on each tank that I can reach while in flight and if parking on a slope or as needed I would shut off the valve on my left tank which did not have the vent line back to the header tank in it, Solved the problem. I would note that everyone should make sure that they are using the new fuel sight tubes that Kitfox has, The onld one's with the compression fitting will eventually leak and I found at one point I thought my vent tube was leaking fuel and it was the fuel sight tubes, Landed and fixed immediatly and then replaced.

[redbowen]

I have found the best way to remove 100LL blue stains is with 100LL. The dye dissolves very easily with gasoline. Then use your cleaning solvent on the area to clean the fuel.

[jtpitkin06]

I also noticed the see through vent line from the header tank back to that wing was full of fuel, is this how it should be? Peter

Observing fuel in the header tank "vent line", on aircraft equipped with wing tanks, is normal.

The line should be re-designated as the "header tank fuel level equilibrium hose." You may see a little bit of air in the hose but it should be approximately the same level as the fuel in the tank.

If you see a lot of air in the equilibrium hose with the engine running, and the tanks are not empty, it indicates your normal fuel supply line may be restricted.

John Pitkin
Greenville, TX