1965 Fuel Tank Filler Neck Gasket... Sealant???

[James W.]

I'm restoring my original '65 Fuel Tank. I know that on a coupe, you have to put the tank up into position before installing the filler neck. My question is, what if anything is the best sealant to use on the tank to gasket and gasket to filler neck mating surfaces?


Thanks in advance.

James West

[Leif A.]

Re: 1965 Fuel Tank Filler Neck Gasket... Sealant???

James,
Sealant is not necessary on the gasket. I might suggest a thin coating of Permatex black on the tank side of the gasket to hold it in place as you re-apply the neck and screws. There are integral seals on the screws and I suggest replacing those screws. They are GM #3767804 and should still be available.
When it's finally time to drive her again, might I suggest that you don't overfill the gas tank. You will most likely never see any seepage whatsoever.

[Mike T.]

Re: 1965 Fuel Tank Filler Neck Gasket... Sealant???

James - A number of years ago, I was replacing that cork filler neck gasket on my 66 L79 Coupe, and since I hate leaks, I decided to apply a light 'smear' of the Red RTV. I consider myself to be a careful mechanic...most of the time. A few days later, I happened to filling up the tank when I noticed something 'down inside' the tank. The gas had reacted to the RTV and turned it into a soft goo. I was able to remove the 'goo' and then figured it might be time to read the fine print on the Permatex Red RTV tube. It reads: NOT recommended for Head Gaskets on parts in contact with Gasoline'. Lesson learned.

[Owen L.]

Re: 1965 Fuel Tank Filler Neck Gasket... Sealant???

While not a C2, I replaced the cork between the tank and the neck on my '72 last summer. I used a new cork gasket and put a thin smear of Permatex gray (fuel contact) sealant on all 4 contact surfaces. I also went to my local Ace hardware store and picked up very small o-rings to replace the cracked/split factory o-rings under the screw threads of the neck bolts. Old ones came off easily with a dental pic; new ones just slid right into place.

[Joe L.]

Re: 1965 Fuel Tank Filler Neck Gasket... Sealant???

James - A number of years ago, I was replacing that cork filler neck gasket on my 66 L79 Coupe, and since I hate leaks, I decided to apply a light 'smear' of the Red RTV. I consider myself to be a careful mechanic...most of the time. A few days later, I happened to filling up the tank when I noticed something 'down inside' the tank. The gas had reacted to the RTV and turned it into a soft goo. I was able to remove the 'goo' and then figured it might be time to read the fine print on the Permatex Red RTV tube. It reads: NOT recommended for Head Gaskets on parts in contact with Gasoline'. Lesson learned.

Mike------


Yes, most RTV's are not resistant to gasoline and many other solvents. The only ones that are resistant are FLUROSILICONES. These are not generally available in the automotive aftermarket and are very expensive if obtained through the industrial/aviation marketplace.

No sealer is necessary on the filler neck gasket. GM did not originally use any and none is necessary now. The filler neck flange should be tapped flat at the screw holes and NEW special, gasketed screws should be used. The GM #3767804 screws are no longer available but I think reproductions are available.

My choice: I make a new filler neck-to-tank gasket from a sheet of 1/8" buna-N rubber and use it to replace the cork gasket.