KapsSA

I discovered a tiny leak in the bottom of one of my 78s gas tank. Noticed a brownish residue on the tank and a little bit of sticky residue on top of the plastic spare tire lid. Pulled the spare carrier and cleaned the crud off and noticed the pinhole. It doesn't drip at all but there is just a dot sized wet spot at the hole. Seems the gas just evaporates before it drips, but over a long period of time leaves the noticeable residue. I first noticed this residue 3 years ago but did a less thorough cleanup. Very little accumulation since then.

I've brazed up leaks in tanks in the past but what's the deal with the rubber liner in these tanks? Is the liner water tight(gas tight)? Or more like a baffle. If tight, why would it leak through the tank.
Can I apply heat to the tank? I know about flushing the tank and removing any vapors. We used to run a hose from an exhaust pipe to the tank to neutralize the vapors.

Is there any type of sealer that could be applied from the outside? I've only got about 3 gallons in there now, will be siphoning that out so the dot sized wet spot drys up. Then try some type of sealant if that is an option.

BKbroiler

Are you sure it has a liner? I thought only 75 - 77 had them.

KapsSA

yep, original tank in low, low mile 78

Red 69

Yes, there is a product you can apply from the outside to stop the leak, but I haven't used it. If NAPA or Pep Boys doesn't have it, try your Truck Stops of America; I am advised it is popular among the truck community.

lowbuck72

I once fitxed a pinhole leak like that with JB Weld from the outside, worked like a charm. ( I use the quick drying JB Quik)

dodge_ss/t

weld it

...Roger...

Are you sure it gas leaking from it? If it is the liner has a leak.Could it be moisture? If you heat the outside to solder it whats that going to do to the plastic liner?Jusst a couple thoughts.

Jughead

I would try JB weld or even mighty putty. I used JB weld on a tank before.

KapsSA

Probed around with a straight pin and found a couple additional pinholes clustered in the area. Rust from the inside. Whatever is leaking is oily, must be gas. How it got out of the liner is the mystery.
Have exhaust and spare removed and the tank straps loose ready to drop the tank. Waiting for my brother to come over for a couple extra hands. Realize I can't weld it because of the liner. Leaning towards dinging in the area(1/2"round) and using Numetal epoxy. See what happens.
If nothing else, new tank.

...Roger...

The way I see it the metal part of the tank just holds the real tank which is the plastic liner.If its not leaking gasoline do you really need to replace or even repair? I wonder if all the tanks with liners maybe form moisture between the metal and plastic and then they rust inside between the 2 surfaces.I have a tank out here I'll go see if I can see any pinholes in it.

KapsSA

The original leak was very minor, but whatever it is it's gummy. I'm still thinking it's gas and like I noted it evaporates as soon as it hits the air and leaves the residue. Over a three year period it left just a few streaks of crud on the lid of the spare tire carrier. With my probeing I'm sure it will leak more now . Regardless, I want to fix it.
Tank is out and cleaned up. Tank sticker in excellent condition.
Is the liner something flexible that can be pulled out? How do they get it in there? Probing the pinholes with a pin I can feel it move but seems stiff. I hit the holes with an air gun and could hear what sounded like the liner collapsing.
With the tank out of the Vette, I can now apply whatever sealer I use easier so that it flows out, instead of working upside down. It'll be somewhat visible between the muffler and tire carrier so I want it to look good.

edit. Could the gummy residue be some sort of adhesive between the bladder and tank?

...Roger...

The liner is pretty hard plastic unlike earlier years that were rubber.I wonder how they made them.

KapsSA

Ya know, I'm starting to think the residue might be some kind of adhesive. It takes lacquer thinner to wipe it off. Paint thinner won't budge it.

68/70Vette

Why not buy a new tank? Quanta sells them. They are not that expensive. Once the old tank starts I think it's a downhill battle trying to save it. I'm not sure the replacement tanks have the rubber/plastic bladder inside, but doens't seem like you really need it as the early C3''s didn't have it.

7T1vette

Patch the holes on the outside, and call it a day! No fuel is leaking out...or it's so darned slow that it doesn't count. Clean the surface with some fine steel wool, then soap/water and dry. Put some 'fuel proof' epoxy on the leak areas and drive merrily along. (The spare will hide the rework.) If you develop a 'real' leak later, then you can buy a new tank.

KapsSA

That's the plan for now. Slightly dinged in the area around the pinholes and gave it a little blast with the sandblaster. Will fill the area and spray it with aluminum engine enamel, real heavy. Then buff the heavy coat of alum enamel with steel wool. Fills in the rough surface from the sandblasting and blends it in nicely.
Discovered that little trick with my trans pan. Sandblasted it and loaded it up with alum paint and buffed it out with 000 steel wool. Looks brand new, not painted.

Mark G

I'd think twice about blasting a gas tank, or even near one. Ever seen sand blasting at night? Sparks like crazy ...like a 4th of july sparkler.

Mark G

KapsSA

Already did it, two little blasts out in the yard. Just enough to rough up a 1" circle for the filler to adhere to.