13 Gallon Fiberglass Tank Neck problem

Folks, I was preparing to add fuel to my right wing 13 gallon tank. I used a flashlight to look into the tank and saw something that concerned me. I reached in with two fingers and pulled it out. I ended up pulling out several piece of what appears to be an old attempt to stop a leak from inside the tank at the neck of the tank. You can see the pattern of the fiberglass on some of the pieces.
I'm thinking this was a "fix" that came loose after reacting poorly with the 93 octane gasoline when I filled it up to the neck during my first flight.
I have not noticed any leaking fuel before this occurrence though the top of the wing shows some possible indications, but I'm too much of a novice to interpret what I'm seeing.
My plan is to drain the tank. Scope it thoroughly for any residue and replace all fuel filters.
Any thoughts or suggestions? Any questions come to mind?
Attachment 11841
Attachment 11842
Attachment 11843
Thank you!

Not saying this is the cause but, I know the marine industry has had issues with ethanol degrading some fiberglass tanks.

There was no fiberglass in this. It was a very sticky substance that was used to seal the neck from the inside of the tank. I'm wondering if the previous owner never filled it up to the neck. He only burned 93 octane, 0 ethanol fuel that he got delivered to his farm from the same supplier that provided his other fuels.

Guess I misunderstood. The 'stuff' in the first photo between the neck and cap looked like fiberglass tape to me.

There appears to be more than one "fix" attempted, here. The amber substance looks like a resin, either polyester or epoxy. the other grey colored material around the neck looks like hysol. If the grey material is somewhat rubbery, then it might be ProSeal.

The fix is to remove any loose material and rough sand the area to be repaired.
Flush with denatured alcohol. Blow dry with an air nozzle.

Use fiberglass mat and West System epoxy to cover the damaged area. I find mat works better than cloth when working blind in a tank. You may have to work with the tank suspended over your head to prevent the resin from dribbling away from the parch when you seal the inside. Let cure and then flip the tank right side up to seal from the outside. Allow West System to cure at least 24 hours before filling the tank.

West Sytem is an epoxy and will adhere to polyester resins. It is very effective in sealing fiberglass tanks. The hard part is getting the area inside the tank cleaned and prepped.

It may take some creativity to make some hook shaped scrapers and sanders to reach and prep the area. Make scrapers from 1/2 inch by 1/8 inch flat steel (Home Depot). Hammer into a "J" shape and grind a sharp edge on the end. Shave and scrape the area to be bonded. With a little perseverance you can reach almost any part inside a tank. If you can't get all the old material off, just overlap with the new stuff by two inches or so. Do the same on the outside.

I think the stuff is Kreem. This notice was attached to each wing tank with my Kit delivered in 1994.

Attachment 11845

The Kreem coating in my tanks is white and translucent. I can see the fiberglass weave of the tank when looking in through the filler neck. It is still holding tight to the fiberglass, however I have never knowingly put alcohol, methanol, ethanol or moonshine in the tanks.

There have been instances of the Kreem flaking off in some tanks. The fix is to remove the wing, put a gallon of Acetone or MEK in the tank, then two people pick up the wing and slosh the solvent around in the tank turning it over and over and such.

Then drain the solvent, refill with another gallon of solvent and repeat until no more Kreem comes out and the tanks look clean inside then reslosh with new Kreem...or, replace the tanks with the new alcohol proof ones from Kitfox.

Years ago I had a leak in the neck of my tank too. At first I thought the gasket on tank cap was worn out and I replaced it but the leak persisted. I took my plane to my buddies hangar, we filled the tanks and pumped air into the leaking tank and discovered the leak in the tank neck.

The repair was just as jtpitkin described. That was several years and hundreds of hours ago and I haven't had a problem since. Obviously after you repair it do a real extensive run up before the first flight, and I spent the first hour of post repair flight within gliding distance of the airport just to be on the safe side.

I ran across this page while looking through the builder's manual. Did the composite of the tank change for 92 to 94? Should I be concerned? Would this warning apply to Ethanol? Attachment 11872

Ethanol is an alcohol, so I would think the warning certainly applies.

I'm wondering if this tank can be sloshed with a solution that will protect it from the alcohol in ethanol. Any thoughts? Folks with older Kitfoxs must be dealing with the same issue.