What Sealant for Inspection Port on Fuel Tank?

[SV Demeter]

I have a big plastic. Inspection port on top of my diesel tank and it was bedded by someone with a silicone based product. The silicone is disintegrating and falling off into the tank creating problems. I'm thinking to use permatex #2 non hardening sealant. It is supposed to be impervious to fuel but figured I would ask here for other suggestions. Thanks

[MarkSF]

I think I would make a sheet rubber gasket - you can buy the raw material at the car parts store (making sure it's a diesel-proof grade of rubber, of course)

[daddle]

Yes. The Permatex is what I use.

[noelex 77]

The problem is once silicone has been used nothing else will stick.
No matter what solvent you use traces of the silicone seem to remain.
If you can mechanically abrade the surface you can get a good bond, but this is difficult with plastic.
Even without silicone not much sticks well to polyethylene. A sealant is viable, but and adhesive sealant often fails the adhesion test.

Can you use a fuel resistant gasket with some mexcanical fixing?

[barnakiel]

Nitrile rubber gasket works OK.

Avoid sikaflex-type sealants as I found them stick for a time then decompose and leak. Perhaps something from Loctite shelf, if you want a spreadable gasket.

b.

[Celestialsailor]

Well...How old was the silicone? Likely, years old. I use it on diesel all the time without issue. My thought is you should scrub your tanks out anyway every 5-7 years. The silicone should last at least that long.

[rebel heart]

Here's the email I got from Permatex when I asked them:

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Many Thanks for your interest in Permatex products . . . . The Ultra Blue P/N 81724 ).. RTV ( Silicone Gasket Makers are not fuel resistant ) .. Permatex makes a product called "MotoSeal #1 ".. it is Impervious...To fuel (Diesel or gasoline )..it is a Polyethylene Rubber ... cures to a rubbery texture. It is recommended for 2 & 4 cycle engines ,especially for motorcycles and chainsaws , and generators (can be added ). Click on Link .........

http://www.permatex.com/products/Aut...Maker_Grey.htm

[SV Demeter]

The tank is fiberglass the inspection port is plastic.will make a gasket and use permatex I think.

[rognvald]

Demeter, I use plumber's gasket material 1/8" to 3/16" and have never had a leak. It is easily replaced, there is no clean up and no chance for stray pieces falling into the tank upon removal. It is easily inspectable since the material will begin to crack as it ages. If the inspection port is a screw in type (as in water tanks) you could use a large rubber o-ring gasket coated with vasoline around the base of the internal threads that seats against the outer flange. These o-rings are available at any good hardware store. Otherwise, the plumber's gasket is your best choice. Good luck and good sailing.

[David M]

Nitrile rubber and Permatex Aviation Form-a-Gasket.

[SV Demeter]

Thanks all. My first problem is getting all the fuel out of the tank. We're on the hook in st Martin and I don't have any Jerry cans plus there may be 40 gal in there. Need to run the tank down low first then pump out rest then clean and rebed.