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Seal Gas Tank

I managed to mostly cut the gas smell in my beetle by basically filling the area where the smell was coming from with hardening foam. However...for other reasons, I wanted to take the tank out and seal it. Make it rust-proof, and fix any pinholes in it so that they would be sealed for good and not contribute to any more leakiness.

I'm very happy to say that as of this writing, April 23, 2010, the gas tank has been fixed, finally, for sure. Yay!

The fix comes in two parts; one won't work without the other. The problems with my fuel system when I got the car were 1) that the fuel tank vent system in th car was plugged. That means that when the fuel expands with heat, the vapors have nowhere to go. I suspect that the vent system plugged firsst, and due to expansion of the fuel vapors, eventually 2) the tank started many small leaks. So basically, the vents where the fuel vapers were supposed to go were blocked, so the leaks formed. The tank was basically venting itself into the luggage compaartment, which is why I could smell gas when I drove the car.

What I did about it:

  • removed, cleaned, and sealed the tank itself
  • replaced all the soft hoses, both liquid delivery lines and vapor lines attached to the tank and expansion chamber
  • unplugged or bypassed the plugged metal vent lines

Before you pull the tank, it's nice to have a stand to set it that holds it with the sump opening at the bottom so that liquid drains out of it. I made a stand out of 2x4s, which worked pretty well. This stand worked well for rinsing the tank to get the gas out, and the drain step for all the parts where I put solution in.

Seal The Tank

Removing the tank wasn't as hard as I thought it would be. Draining it first was at least half the problem. You don't want it to have gas in it, for both vapor and weight reasons. When you get the tank out, THE FIRST THING YOU MUST DO IS FILL THE TANK WITH WATER AND DRAIN IT, TWICE. This gets the gasoline vapors out of the tank. This is VERY VERY IMPORTANT. A tank that has been drained of gasoline is filled with gasoline fumes and air, which is a highly explosive mixtured and will blow up like a bomb.

The POR-15 company sells a tank restoration/sealing kit. I found it nice to use and very thorough. They send you four types of stuff. First is "Marine Clean" which is like a heavy-duty detergent. You use this to clean the crud out of the tank, particularly if it sat for a while with old gas in it. You mix the stuff with hot water, put it in the tank, swish it around, then drain it and rinse it. I used half a bottle of the Marine Clean at a time, I think I mixed it 1:1 or 1:2 with hot water. The first batch came out black, the second was pretty clear. (Each time you do this you seal the tank outlets so that you can swish the stuff around inside.) When it's clean, you'll still be able to see rust residue, but everything else should be cleaned out of it.

The next step is Metal-Ready. It's a mild acid solution that etches the inside of the tank, absorbs the rust, and the entire surface with Zinc Phosphate. This gets rid of the rust in the tank and makes sure the surface is ready to accept the sealant.

The POR-15 sealer itself is interesting stuff. It sticks to metal really well, and forms a thick, hard surface. The only problem with it is that if there's a place that it pools a little, it will form a bubble, which will then break when it's dry. This wasn't a particular problem in my tank, I just vacuumed the tank out after I broke the bubble apart. One thing the instructions left out: the solid part of the POR-15 (what forms the final coating) tends to settle out to the bottom of the container. It's very important to turn the POR-15 can upside-down and shake it a lot to get the solids mixed into the liquid.


I think the general thought is to replace all the soft fuel lines every 2 years. The get hard and brittle with age. The soft lines seal against the metal lines by being soft; when they get brittle they lose their seal and start to leak. Leaking gasoline == bad, for those of you not keeping score at home. You should really replace all the soft fuel lines, even the one that comes out of the bottom of the tank that the tank has to be removed to get to. Yes, that one too.

Sections of liquid gasoline-carrying hose that I ended up with:

  • from the bottom tap of the tank to the under-tank filter
  • from under-tank filter to the tunnel pipe at front
  • from tunnel pipe at rear to filter at rear
  • from rear filter to front engine tin fuel line pass-through
  • from pass-through at front of engine to fuel pump inlet
  • from fuel pump outlet to carburetor inlet


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