Fuel cap leak

[littlecricket]

Just wondering if anybody has had a fuel cap leak? My friend’s did and stained his fabric... Just wondering how prevalent they leak and of any preventative measures in the future. Thanks.


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[DesertFox4]

A couple things can cause that big of a leak. First the gasket may be damaged or aged and no longer seals well.
That is a somewhat common issue after sometime in service. Years ago a solution was discovered that takes care of this issue. Rubber gaskets are used with the stock caps. They lose elasticity over time and don’t seal well. I’ll attach photo of a permanent solution. It is a blue gasket available through Mercedes dealers. The photo has the part number on the package. This gasket is somewhat thicker than the stock gasket and you may need to adjust the tabs on the caps due to the thicker blue gaskets. This blue gasket does not seem to age and lose shape or elasticity or be affected by fuels. These gaskets have solved many cap leaks over the last 18 years or so. I installed a set in my first Kitfox 16 years ago and they are still in service with no leaks. I hope they are still available from Mercedes under part number 140-471-00-79-493 (tel:140-471-00-79-493)
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Secondly you can J.B. Weld shut the underside of the crimped rim of the cap and the four tiny “vent” holes found on the rim of the cap. Not the ram pressure tube hole in the center of the cap that is there to help pressurize the fuel system in flight. Either one or both of these fixs should end the fuel leaking during flight. Likely the first fix will take care of the problem. Hope this helps. I do these modifications to my caps and have never had cap leaks.

[jiott]

I agree; have those gaskets on my Kitfox also.

One other possibility-it could be overflow from the vent tube caused by:

Parking on uneven surface with full tanks, possibly in hot weather.
Flying with full tanks and ball not centered or one wing low. A friend of mine was following me one day as I flew carelessly with ball not centered and full tanks, and he observed a steady stream of full coming out of my vent tube. Quite a stain on my wing when I got home.

[Dave S]

Jim & All,

Very much agree that a person can get fuel to exit the cap pitot even though the cap gasket is perfect.

I discovered a couple additional ways to dump fuel out the pitot.

1) Maybe this won't happen with a tailwheel taxiing; however, on a trigear if a person makes a tight turn at low taxi speed with full tanks, it is easy to squirt a bit out the pitot due to the centrifugal force on the fuel in the tank.

2) On a maximum slip with full tanks - ditto. Wondered why I smelled fuel once following the slip - The stain on top of the wing pointed directly to the tail access cover - even a few stains on the TAC evident. The natural air flow back from the tail cone guarantees the odor will be pulled forward.

Oh well....

[jiott]

You're right on Dave; I have had that happen to me several times in a slip.

[littlecricket]

Yeah, it was weird. First leg full tanks no leak. Second leg 2/3 down to a 1/4 by the end, but more yanking and banking it leaked. Pretty bummed, 10 hours on the plane and now have stains on the Oratex wings. Thanks for all the info, I appreciate it.

[Shadowrider]

Sorry about the stains. Anything you can do? Did you wax the wings with Oratex wax? Wondering if that helps at all? What color are your wings?

[jiott]

I wonder if this staining thing is the Achilles heel of Oratex? Everything else about it seems to be so good.

[efwd]

If I'm not mistaken, fuel stains painted planes as well.

[littlecricket]

Yeah, the wings had fresh wax. Only 9 hours on the plane...:mad: Always hangared. Lars thinks the stains may fade over time... Going to try a few more things to remove the stains. If stains stay, might do a light dusting of paint to cover them up. Not sure about white wings if to do again...

[Esser]

If I'm not mistaken, fuel stains painted planes as well.

Not urethane

[Dave S]

One of the main reasons I used Aerothane over Polyfiber was the durability and resistance to staining of almost any kind. Bird dooey and any other species of feces, pine sap, fuel, oil, tar just about any kind of gunk I have had the misfortune of collecting on our kitfox has always come clean 100%. On several occasions I had to use MEK on a rag as the solvent of choice, which is just fine with Aerothane provided there are no breaks in the paint film. Polytone is easy to repair but not so good in dealing with stains. Each product has its advantages and disadvantages. Marketing people generally don't share the disadvantages with great enthusiasm but are very passionate about the plusses. :rolleyes:

[HighWing]

Steve's thoughts are right on. I recall when the blue Mercedes gasket was mentioned in one of the early e-mail lists. I bought them then and they did save a lot of grief for lots of guys. Then the vent hole thing is spot on as well. My 1992 cap has the two holes in the top of the cap welded shut. These were there for venting the gas tanks of the Mercedes cars. With our set-up if not sealed they will neutralize the pressure provided by the Pitot vents and allow spilling in all the attitudes mentioned including light turbulence with full tanks. I think I found some of the blue gaskets on ebay and ordered a couple as mine are the typical black replacements. I will report when they get here if they are actually the ones mentioned.

[efwd]

I wonder if this staining thing is the Achilles heel of Oratex? Everything else about it seems to be so good.

came back across this question. I have Oratex now for 3.5 years using 100LL 100% of the time (490hrs). I get white residue from the exhuast that trails back to aft of the pilots door. It washes right off. Dustin certainly had me concerned with his experience but mine is proving to be different.

[SwoffDaddy]

Do you use a lead scavenger, such as decalin?

[efwd]

I do use Decalin.
I have had the fuel flow from the vent in large qty as well and I have not had fuel stain the silver Oratex on the wing nor has it stained the white Polytone paint. I thought for sure the white was going to show but it wiped off with alcohol as well.

[SwoffDaddy]

I do use Decalin.
I have had the fuel flow from the vent in large qty as well and I have not had fuel stain the silver Oratex on the wing nor has it stained the white Polytone paint. I thought for sure the white was going to show but it wiped off with alcohol as well.


could the stain be coming from the decalin/lead exiting the exhaust pipe. That is what I was told mine stain is.

[sonex293]

We're using SuperFlite paint system and E0 UL Automotive 93 AKI Gas has stained our Paint. The SuperFlite folks told us that they haven't seen staining with 100LL but didn't have any experience with E0 UL fuels.

Wish we had some type of check valve that allowed air in and out, but kept the fuel in. We get fuel splashing out even with 3/4 full tanks while taxiing around.

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Michael

[Av8r3400]

I've had good luck using a "Mister Clean Magic Eraser" to remove fuel stains.

[rv9ralph]

You probably need to change the fuel cap gasket. Many Kitfox owners have had good results from a Mercedes gasket.

33306

I hope this will help prevent new staining.

[sonex293]

The fuel is actually coming out the vent tube not around the/through the gasket. Probably doesn't help that its a nosewheel.

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Michael

[jiott]

Anytime you do a slip, skid, or other uncoordinated flight maneuver the fuel in the tanks will slosh sideways and very likely burp some out of the cap breather vent tube, especially if the tanks are nearly full. Its a nuisance that can't be helped if you are like me and do a lot of intentional slips. I have to wipe down the wings aft of the fuel caps after almost every flight or two, otherwise a fuel stain will start to show.