TECH TIP Technical Index

Fuel Tank Repair & Restoration

Itís a beautiful sunny Fall day. The weather couldnít be better. You are cruising along in your VW with a big smile on your faceÖuntil the dreaded happens, that is Ė the engine dies like you just reached up and shut the ignition off. The smile quickly vanishes from your face as you coast to the side of the road, wondering what went wrong THIS time. First, you try to restart the engine, but it wonít hit one beat even after five minutes of cranking. You get your buddy to twist the key as you pull a plug wire and check for a spark. OWW*@&#!^%. Yep, youíve got a spark. You take the fuel line off the fuel pump and tell your buddy to crank the engine Ė no fuel is coming out but the tank is full because you filled it up at the local in-n-out just an hour ago. You know the fuel filters are clean (the one at the engine and at the fuel tank) because you replaced them the day before yesterday. Wait a minute Ė this has happened to me for the third time in the past two months. Iíve serviced everything except the gas tank itself!

Fuel Gauge

Hey Ė after 20 or more years, there is a good chance that moisture buildup inside the tank has caused scales of rust to form and eventually clog the pickup tube. What do you do now? Well, you have a few choices. One way is to simply buy a new gas tank. While not always the most cost effective, you eliminate the problem until the rust forms again. Of course, if there are already holes in the tank, you need to replace it anyhow. Another way is to remove the tank, drain it completely, and take it to a radiator shop to have it boiled out. Problem is, not every radiator shop will do this. If they do, the charge can reach around $75 or so. New tanks usually donít cost that much more. If you have a rare tank (Ď40ís or Ď50ís) a new one probably would not be an easy option. Which leads the third solution Ė and the one I chose Ė buy a fuel tank restoration kit (about $30 or $40) and do the work yourself. You can get these kits from Eastwood or J.C. Whitney. Let me explain the kit for a second. It includes the following:

  1. Phosphoric Acid (the same stuff thatís in naval jelly that eats rust off your barbeque grill)

  2. Acetone (etches the inside of the tank after the acid bath, in preparation for the tank coating)

  3. Tank Coating (coats the inside of the tank and seals it against further corrosion)

Now I will tell you how you can get the first two chemicals separately, because the kits supply just barely enough to get the job done. Warning first: if you decide to buy the phosphoric acid separately, it is in a very strong undiluted form. You must dilute the acid with water around 1:1 ratio before using it in the tank. Wear heavy-duty thick latex gloves when handling this stuff, and I suggest eye protection in case the stuff should splash anywhere but down. Now I donít want to scare you with all this, itís just much better when you donít spill the stuff on your skin or in your eyes Ė treat it like any other chemical you deal with on an everyday basis Ė with caution. Use both the acid and the acetone in well-ventilated areas so the fumes donít get you. Both the phosphoric acid and the acetone can be purchased up to a gallon at most hardware stores and maybe at the local Wal-Mart. The fuel tank coating is available by itself, and there is plenty in the quart can. Some other things youíll need besides the proper tools to remove the tank are:

  • Vacuum caps to plug all the small outlet tubes (from auto parts store)

  • Duct tape to cover the fill tube and sending unit hole (hardware or discount store)

  • Isopropyl alcohol to absorb water after washing out tank (discount or drug store)

  • Siphon device to drain fuel out while tank is still in car

  • Buddy to help with project (not necessary, but makes work easier)

Now, first things first Ė DISCONNECT THAT BATTERY! I know you donít normally do it, but when you are fooling around with gasoline fumes, better to be safe than sorry. Before you drain the tank of gasoline, be sure you have enough containers to put in 11 or so gallons of gas. Using a siphon, drain the tank from the top. Then remove all the hold-down bolts and the sending unit wire. Lift the tank far enough to disconnect the fuel line. As soon as you do this, put the vacuum cap on the outlet to keep anymore fuel from spilling all over your paint and everything else. Once the tank is out, drain all the remaining fuel and remove the sending unit.

Next, plug all the rest of the outlet tubes with those vacuum caps. Take the tank to a self-service car wash and thoroughly and forcefully wash it out until you see no more rust flakes coming out as you drain it. As soon as you get back home, take two bottles of the isopropyl alcohol and pour them in the tank. Slosh the alcohol around the tank for a minute or two. Then drain the tank completely.

Now take the phosphoric acid and read the label on the container. If it has different dilution ratios according to how itís being used and you find a similar application on the label, use it. Otherwise a 1:1 acid to water ratio should do just fine. This will be stronger than the solution in the kit, but not so strong as to cause damage to the tank. Pour enough solution to cover the sump area and then above it about Ĺ inch or so. Put duct tape over the fuel filler neck and the sending unit hole and slosh the solution around vigorously, making sure it gets to all the inside surfaces of the tank. Let the tank sit on a level surface for at least eight hours, preferably overnight. After this much time, take the tank and drain it completely. Wash the tank out thoroughly with your garden hose. Taking a flashlight, inspect the inside of the tank. It should look like new or almost so. If there is still a significant amount of rust (other than surface scarring from previous rust), repeat the above acid step using less water to dilute (about 1: .75 or so acid to water).

Got all that pesky rust out? Good! Now itís time for the acetone. Phew! This stuff smells like fingernail polish remover Ė because thatís exactly what itís used in. Pour a couple of quarts of the acetone and slosh it around (remember to seal off the inlet neck and sending unit hole). This will remove leftover moisture and etch the inside so the tank coating will stick well.

Immediately after draining the acetone, pour all the tank coating in and slosh around for about five minutes (seal the inlet neck and sending unit hole). Follow the instructions on the can. Each brand or type may have slightly different application procedures. Pour the excess liquid out and let the tank sit overnight to cure the coating (inlet neck and sending unit hole left open now). Reinstall the tank the same way you took it out. If your fuel gauge sending unit is bad, now is the time to replace it with a new one. After the new tank is in and all buttoned up, pour the gasoline back in (if you had rust in the gas, filter it out before pouring it in). Donít be alarmed if the gasoline changes the color of the tank sealer. Some of these sealers change color as the fuel hits it and further cures the coating.

As a further note if you chose to buy a new tank Ė it is recommended that you coat a new tank with the sealer. Just follow the above acetone and sealing steps. You wonít need the phosphoric acid for the new tank.

Also, if you are restoring your old tank or had it boiled out, you will need to repaint it with a quality paint of your choice. I personally like Rust-Oleum paints since they are tough as nails when dry.

Hopefully, this tech article will help you solve the unpredictable stalling problems, fuel starvation problems, or the no-fuel problems that you seemed to have before.

Your VW giving you fits, got bugs in your Bug, got a Super Beetle-specific problem? E-mail me at .

Your VW Maniac & Tech Specialist

Mike C.