Gasket sealant for diesel, Recommendations?

Does anyone have recommendations for gasket sealant for inspection ports/sumps in diesel fuel tanks? The sealant will be exposed to liquid diesel continuously.

We have fiberglass fuel tanks, approximately 3/4" thick. At the bottom of each tank there is a sump bolted to the fuel tank, from which any contaminated fuel can be drained off. We've owned the boat for two years now, and although we've drained regularly, we haven't gotten any gunk at all.

The issue is that fuel is seeping through the seal and dripping onto absorbent pads. The forward tanks sumps were removed, and gaskets replaced using some type of sealant, that looks kind of like the red permatex that comes in a can, but I'm not sure. The fwd tank sumps don't seep at all.
The aft sumps are more difficult to get to, and the sumps haven't been resealed.

I wrote Permatex for recommendations, but haven't received a reply.

Anyone got any ideas? I've asked a few stores, but can't find anyone who really knows anything. One guy even recommended silicone . . . I kid you not . . .

When I bought my boat 35 yr ago the alum. tanks leaked at the fittings. Of course I had to empty the tanks one at a time.

I used Aviation Form a Gasket and nary a leak since.
If is black, gooey and messy but not a problem since.

My tank fuel supply fittings are at the tank bottom so have been exposed to diesel for 35 yrs. I realize the exposure of mine may be minimal compared to yours but the Form a Gasket was developed for use in situations like this, fuels and oils.

THe areas to be sealed MUST be clean of diesel though. Fiberglass may need some sanding and a very good wipedown with a product like Brakeclean to remove any diesel residue.

In your case, I assume you bolt the sumps to the tank, the bolts and threads, including any internal threads, will also need to be sealed and CLEAN of any diesel residue.

Any oily residue will defeat even the best sealers.

C lectric:

Permatex Aviation Form A Gasket , part # 80019 is what I had found as well. It states in the description "Resists gasoline, oil, and grease". Diesel is an oil, but I was a little turned off that it didn't state diesel specifically. Your experience goes a long way to changing my mind! Thanks for taking the time to reply.

Permatex rep came back with either Permatex Aviation Sealant for the gasket, or Permatex Permashield fuel Resistant gasket dressing 85420. I'm probably going to go with the Permatex Aviation Sealant. Thanks for the help all!

C lectric said:

When I bought my boat 35 yr ago the alum. tanks leaked at the fittings. Of course I had to empty the tanks one at a time.

I used Aviation Form a Gasket and nary a leak since.
If is black, gooey and messy but not a problem since.

My tank fuel supply fittings are at the tank bottom so have been exposed to diesel for 35 yrs. I realize the exposure of mine may be minimal compared to yours but the Form a Gasket was developed for use in situations like this, fuels and oils.

THe areas to be sealed MUST be clean of diesel though. Fiberglass may need some sanding and a very good wipedown with a product like Brakeclean to remove any diesel residue.

In your case, I assume you bolt the sumps to the tank, the bolts and threads, including any internal threads, will also need to be sealed and CLEAN of any diesel residue.

Any oily residue will defeat even the best sealers.

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Are you saying that you have owned the same boat for 35 years? Amazing.

Comodave said:

Are you saying that you have owned the same boat for 35 years? Amazing.

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Have owned the same boat since 1981, 42 years. Wife would divorce before letting me sell LOL! I have rebuilt the engine 4 times, rebuilt the transom and replaced the outdrive, well found another when hitting a submerged log at night that tore it off the transom and then replaced it. In 42 years only hit 2 things at night. We spend more night boating than most people do daylight boating.

We have gone through 24 boats in 52 years that we have been married. I can’t imagine having one for over 40 years. I guess different strokes…

I've owned the same car for 47 years...

RT Firefly said:

I've owned the same car for 47 years...

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But do you do all your normal driving in that car, as compared to doing all the normal boating in one boat?

Comodave said:

But do you do all your normal driving in that car, as compared to doing all the normal boating in one boat?

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I guess I should qualify. We have owned 21 boats ( that I can remember off hand) over the years. But in 1981 we found the 1976 26ft daycruiser that has fit so many needs. It has trailered to Canada and done BC, trailered to San Filipe and cruised inside of baja, done Cheasapeake, cruised out to 140miles in the Bahamas, and the Powell and Mead lakes along with offshore Ca to Monterey and Santa Cruz. While having the other boats at times to fit certain needs, we have always kept the daycruiser that sits on the hydrohoist behind the house. Right now we have 4 boats in Ca Delta, and 2 in Hawaii. Just when we found the 26fter, it has been one of the most fun boats we have had. Can't explain the feeling of firing up that big block and cruising at a sedate 30mph to B'fast or dinner in the Delta. Oh, yeah, I still have a '62 Willys CJ5 Jeep bought new by the first mate's dad when she was a girl. I plead guilty of keeping things for a loooooong time LOL!