fuel weep out of cap

[Larry Martin]

I have new caps on the way, but just wanted to insure all else is ok. I fill the tanks with warm fuel to the brim. The next day, it is still to the brim, no vent leaks, etc. Go fly and upon return, one tank cover has a bit of blue dye weaping out. Is this just the cap? The caps do have some resistance when locking down, but on the advice of a friend who is unaware of this "weaping" cap suggested that I get the "good" caps from Webco. So I did. All fuel gauges, etc are normal, so am I correct in blaming the cap?

Thanks

[LeWayne Garrison]

Probably the caps. Soaking the rubber in MEK will soften the rubber a couple of times, but eventually it gets too hard to seal correctly. Other possibility is there is usually some fuel spilled in the fuel door area. If you fly before this has dried it will suck out around the door (not necessarily the caps) and stain the wing. Have also seen this happen with dried fuel in the door area after a rain, where small amounts of moisture liquidate the stain and allow it to stain the wing

[JIMICS2452]

First try tightening the cap. If that does not work give it a soak in lacquer thinner or acetone, Stay away from MEK, it will cause the cap to loose elasticity over time and is really nasty stuff health wise.

[AlanBreen]

If you're getting new caps from Webco get the fuel flap (door) seals as well.

It's worth replacing these regularly, it stops rain seeping into the cap area helping reduce the chance of water getting into the tanks, especially the Aux tanks on the Twin.

Also a well sealed flap will reduce the possibility of the cap seeping fuel in flight. The suction caused by the low pressure area on top of the wing is prevented from acting around the fuel cap.

[Don Ostergard]

I have had the Webco caps on the mains of my 250 for a couple of decades now and the grey rubber-like seals are beginning to lose their supple nature. Before I order new caps, I'd like to try to rejuvenate the ones I already have in lacquer thinner as recommended in this thread. (I don't like working with MEK or acetone.) While the comments have been helpful no one has mentioned how long one should soak the caps in the rejuvenating lacquer thinner (or other). 10 minutes? An hour? Overnight? I expect one can overdo it.
Thanks,
Don Ostergard, ICS 3263

[N3322G]

I've used both the Webco screw type caps and the original-like thermos-style caps.

I prefer the thermos style for two reasons 1. No matter how firmly inserted/attached, a lever can always get them open as opposed to the Webco caps which under some circumstances are difficult to remove. 2. The thermos fuel caps seem to last longer - no data on this - just perception

[LeWayne Garrison]

To clarify, acetone and MEK (MethylEthylKetone) are very similar chemicals. MEK is only a slightly longer chain ketone than acetone. Neither is particularly toxic, although you would not want to ingest either. Lacquer thinner is a much more complex mix of toluene, ketones, esthers and ethers and also containes MEK and is a much more toxic compound. All would probably soften the rubber in the fuel caps, although I have always successfully used MEK. Soak for and hour or two, timing is not critical. MEK evaporates rapidly and attracts water vapor, so after much longer than that you won't have much MEK in the solution anyway. The comment above about eventually the rubber won't soften after a few treatments is correct.