Leaky fuel caps costing me $$$

brian1983lucas

I have 1964 PA-28 Cherokee that has a consistent problem of losing fuel from both of the gas caps during climb out. I have replaced the rubber seals under the caps, and even purchase new caps from Spruce, but still find blue streaks on the wings after each flight when I land. An obvious answer would be to just not put as much fuel in the tanks and just fill to the tabs instead of topping off the tanks, but I do make some pretty long cross country flights where I need the fuel, so I usually keep the tanks full. I have searched the Internet for different fuel cap solutions, hoping to find something that is flush mounted and/or seals tightly to prevent this from happening but I haven’t been able to find anything but the stock caps.

Does anybody know of a solution to this problem, and where I might find a better gas cap?

Brian Lucas
N6234W
‘64 Cherokee

Jmcmanna

I am not an expert, but I think I remember hearing that there are two different thicknesses on the available rubber seals. Maybe there is a different sized seal that you need.

brian1983lucas

I’ve only been able to find one size of seal through Spruce or other retailers, and have tried a couple different ones to see if they’re just manufactured differently, but they still don’t fix the issue unfortunately.

Scott Sherer

Hi, there are two thicknesses and I've purchased the wrong ones twice on two different airplanes. Check your parts manual for the right one. https://www.aircraftspruce.com/catalog/eppages/gasket08-13788.php?clickkey=3008203 https://www.aircraftspruce.com/catalog/eppages/gasket08-13787.php?clickkey=3008203 Here they are, two different thicknesses.

brian1983lucas

Scott, the second link you sent isn’t the correct diameter size and won’t fit my cap. I haven’t been able to find a gasket thicker than 1/16” with the correct 3” OD x 2” ID size.

Is there not a better fitting cap on the market that locks in place and seals properly?

Scott Sherer

Hi Brian,
To the best of my knowledge there are no alternate sources of tank covers other than buying them directly from Piper/Aviall. I've looked for years and haven't found anything. Perhaps someone else has. If I remember right, Piper charges a couple of hundred for new ones.

kkleinberg

Just checking if replacing the fuel tanks seals is approved as user Maintenace? If you do it, does it require a log book entry?

griff390

https://piperowner.org/talk/discussion/comment/1445847#Comment_1445847

Kkleinberg:

No matter who performs the work, a log book entry is required.

Here's a link (below) to a synopsis of user maintenance items, however, the actual regulation is under: 14 CFR Part 43, Appendix A, Subpart C. It's a bit different from the pamphlet.

https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56398/FAA%20P-8740-15%20Maintenance%20Aspects%20of%20Owning%20Your%20Own%20Aircraft%20%5Bhi-res%5D%20branded.pdf

Gaskets are not specifically included under owner maintenance, while more complex jobs, such as servicing wheel bearings are. My best guess is if they allowed "gaskets", people could interpret that to include gaskets on the engine or a hydraulic landing gear pump.

To be legal, just replace the gaskets and have your A&P sign it off. Done.

asikora1

Maybe this?

https://realgaskets.com/product/fuel-cap-gasket-piper-cherokee-3-od-x-2-1-8-id-x-1-8-thick/

MikeJJ

OK, thinking out of the box...maybe it is not your actual seal that is leaking. Two things come to mind. I have seen some caps with vent holes in the cap, mostly on Cessna aircraft. If the check valve in the vent is not working, fuel will leak out. Did someone in the past put one of these on your Cherokee?

Another thought is that there have been instances where Cherokee filler neck corrosion in the area where it joins the wing skin can get bad enough to to allow fuel to leak out. In this case the filler neck must be replaced.

One last thought, When you twist the cap closed, there should be a definite gradual tightening of the seal. Perhaps the mechanics of the cap are not working as it should. The shape of the ears on the cap or the mating surface inside the filler neck may have worn to the point where a proper seal is not possible without replacement.

Regards,

Mike

djspathis

https://piperowner.org/talk/discussion/154010/leaky-fuel-caps-costing-me

Can you verify that the blue streaks you're seeing are ONLY from the fuel filler opening and not near any wing skin seam? If near a seam, you may have a leak somewhere else (inside the wing) and the low pressure on top may be drawing the leaking fuel out. Please clarify.

DJ

empannin

DJ, good point. There is also a top of tank seal going to the filler. I had the shop replace one of these at annual early on.

AndyGoldstein

I had a leak like this that also turned out to be the packing between the filler neck and the top of the tank. (1966 Cherokee 180.) I initially tried new gaskets, then a thin Teflon shim under the gasket, and continued to get a blue streak off the filler.

What fixed it was LocTite 290 (the watery green type that is used to penetrate fasteners in place). While the fuel level is at least an inch down, dribble a little LocTite 290 into the junction between the filler neck and the tank skin. Let it soak in and replenish a couple times, then let dry before refilling the tank.