How To Repair A Rusty Gas Tank

Article by Mark Trotta

Finding a suitable replacement gas tank for a vintage small engine is not always possible. Sometimes, the only alternative is to repair the one you have.

When I acquired this Tecumseh H25, all of the engine tin, including the gas tank, had surface rust. Looking through the gas cap opening, I could see light surface rust on the inside.

repair a rusty gas tank on vintage tecumseh engine

Closer examination revealed a small pinhole on a bottom corner of the tank. After looking for a replacement for nearly a year, I decided to try repairing the tank myself.

Stripping Down To Bare Metal

A bench grinder with a wire-wheel quickly removed the majority of the old paint. For the hard to reach places, I used a piece of Scotch-Brite pad.

Cleaning A Rusty Gas Tank

To remove the grit and dirt and loose rust, I started with a dab of household dish detergent in some warm water and poured it into the tank.

After hand-shaking the tank around for a minute or so I drained it out, noticing the now-brown colored water. I repeated this process several times until the water poured out a little clearer.

Repairing A Small Rust Hole

If you have a small pinhole leak in a metal gas tank, a two-part epoxy should work for you. But any larger than that, soldering or brazing may be a better option.

If the tank has heavy pitting or there are several rust holes, welding is the best solution. Repairing or replacing sheet metal is a difficult skill and requires either a MIG or TIG welder.

I was fortunate that there was a just one small pinhole on this tank. What also helped was that the original sheet metal was pretty thick.

J-B Weld Gas Tank Repair

I've had good luck with other J-B Weld products, so I bought their gas tank repair kit #8217.

The epoxy is a two-part, hand-mixable, non-rusting putty that is also petroleum-resistant. It can be used on plastic or metal gas tanks.

Before applying the epoxy to the tank, you want the surface to be totally clean so the putty will adhere. After the tank is as clean as you can make it and dried off with compressed air, scuff the repair area with Emery cloth.

Shop: J-B Weld Gas Tank Repair

Two-Part Epoxy

Kneed two equal parts of the putty together until you get a uniform color, then apply. There's plenty of time to apply the epoxy, so go over it several times using firm pressure.

Directions say it cures in two hours, but I waited overnight before continuing. After the tank was tested by filling with gas and checking for leaks, I sanded down the epoxy with a coarse file and Emory cloth.

Removing Rust From Inside A Gas Tank

I've had good results with vinegar in the past, so I decided to try it in the rusty tank. After filling the tank half-way, I shook it up a little and let it sit for three days.

When I poured it out, I was disappointed that the vinegar didn't do much at all. Apparently the rust was too heavy for the vinegar to work. Before going to Plan "C", I refilled and rinsed the gas tank with hot water soap several times.

Does Evapo-Rust Work?

A while back, I watched a YouTube video where a guy soaked a rusty old knife in a container of Evapo-Rust. It seemed to do a good job with the old knife, so I decided to give it a try.

Evapo-Rust is non-toxic and biodegradable, and has no fumes or bad odors. It's also non-corrosive, so it's safe if you accidentally get some on your skin or in your eyes. Evapo-Rust is offered in quart (32 Oz) and gallon (4 Qt) sizes.

Shop: Evapo-Rust Remover

On the back of the container it gives instructions on different ways to use it, including how to de-rust a small gas tank. I poured the quart of Evapo-Rust into the tank and it took every last drop. (So now I know this little gas tank holds a quart of gasoline.)

The directions advise waiting two to four hours, but I let it soak for three days. I figured I'd be patient and let the chemicals do their job.

NOTE: Evapo-Rust is water-based and environmentally safe.

Evapo-Rust can be re-used several times, so I just poured it right back into the quart jug it came in. After the tank was empty I looked inside, and was really surprised at how well Evapo-Rust worked. It probably helped that I let it work for several days.

Prime and Paint

Before I primed the gas tank, I cleaned it with brake parts cleaner, then dried it thoroughly with compressed air. A light scuffing preceded the primer coat.

Several days later I applied the color coat. First I lightly scuffed it with a Scotch-Brite pad.

I waited a couple days, wet-sanded the first coat with 400 grit, then shot a second coat.

NOTE: Depending on where you live, the inside of the gas tank may start to rust up again if not in use. If you're not going to be filling the tank with gas right away, coat the inside with a light oil to prevent rusting. When ready to use, simply rinse out the oil by sloshing a little kerosene or gas through it.