Tips for repairing plastic gas tanks

Question:

I know that my question isn’t directly car-related but a response could be applied to certain car parts as well. I restore old snowmobiles and have not come up with a good way to repair plastic gas tanks. I have tried the plastic welding thing with limited success. Any ideas?

Answer:

As you probably know, there are plastic welding gun kits available for about $200 from local suppliers or the Internet that work very well. Just read the instructions and practice until you feel confident enough to fix your tank. And there are also sealers like Versachem (part 9025) sold at AutoZone stores that they say will do the job. However, with a little practice you can do the whole thing yourself using a cheap small soldering iron and a bit of American ingenuity. Here’s how:

Things You’ll Need:

0 3M 5200 polyurethane adhesive O Fiberglass patch

O Sandpaper

O Shop cloth

O Dishwasher detergent

O Eye and hand protection

O Respiratory mask

O Soldering iron

O Old plastic oil bottle

First, remember that used fuel tanks are big bubbles of gasoline fumes that will explode if ignited. So don't be tempted to take shortcuts to save time, and if you are the impatient accident-prone type, buy a new tank. Any time you mess with heat and gasoline you run a risk if you don’t manage things carefully. Use protective hand and eye gear, and a respiratory mask while working.

Wash your tank inside and out with hot water and dishwasher detergent; let it dry thoroughly for a day or so with the filler cap off, and then do it again. If the necessary repair is high up on the tank, you can even fill the tank with water to just below the repair as an extra precaution, or you can put in water and turn the tank upside down so that the area you will be working will be out of the water.

Use the soldering iron (the little cheap ones are best for this job because they don’t operate at very high temperatures) and create a small C4") hole at each end of the crack to prevent it from cracking further. Next, use the soldering iron to heat the plastic to a semi-molten state along the crack, and sort of stitch and swirl across the crack while pinching it slightly to seal it up. Take your time and don't leave any holes. Test your tank by filling it with water to check for leaks. Fix any that you find using a bit of plastic from somewhere else on the tank, or if necessary, plastic from a plastic oil bottle. (They are made of the same petroleum-resistant plastic as your tank.)

At this point you will have a trough-like scar that seals, but is pretty frail. You can fill this with more plastic, or if you are looking for resilience, lay a very thin piece of copper wire into the scar, and work oil bottle plastic into and over the crack. The wire acts like rebar in concrete and holds it together. Finally, you can use 3M 5200 polyurethane adhesive and a patch of fine fiberglass to further reinforce the crack if you suspect the tank will be subjected to rough treatment. You can then sand and paint your fix with flexible plastic paint to make the fix less noticeable. Don't be tempted to just use a fiberglass patch without the soldering iron welding job though, because fuel will work its way along the fiberglass threads and you will still have seepage.