Tech: how to repair a rusty fuel tank

Your streeter enjoys drinking from a rusty tin even less than you do. It’s time to fix the fuel tank

Photographers: Andrew Clatworthy

When people are rebuilding or restoring their streeters, one item that often gets overlooked is the fuel tank. Sure, you can give it a quick lick of paint but that’s like polishing a turd and is more likely to cover up problems rather than fix them. Like the rest of the car, your tank will need some refurbishment.

Decades of contaminated fuel can eat away at the insides of your fuel tank, especially if the car has been sitting for a long time. Petrol leaves heavy deposits of a varnish-like substance that’s also a perfect moisture-trap. You wouldn’t drink from a rusty bowl, so don’t expect your car’s delicate fuel system to cope very well either.

First published in the April 2007 issue of Street Machine

This leaves you with several options: buy a new-old-stock replacement (for most old cars these are on the shelf, right next to the rocking-horse poop); fit an aftermarket alloy or stainless steel unit; or restore the original.

If you’re striving for that authentic look, restoration is easily the best option. Let’s see what’s involved.


1. If your original tank is heavily dented or full of rust holes, try to find a better example to work with.

Most factory tanks have a lead or zinc finish to protect them but check for fuel stains around seams and for pinholes with a reddish or oily stain around them, as what appears to be a sound tank may be heavily corroded on the inside.

2. Before beginning any restoration, your tank needs to be thoroughly cleaned inside and out. Chemical cleaning is effective; simply take it to your engine reconditioner for a 24-hour soak in the caustic tank.

Not only will it come out squeaky clean, it’ll also make the task of treating the tank’s insides a lot simpler.

3. It’s not uncommon to find small dents like these on any tank that’s been in service for more than a few years.

While it might seem tempting to simply fill them, tank flex from sloshing fuel usually dislodges thick filler applications over time. For a long-lasting finish, a proper metal repair is the best option.

4. It’s bloody hard to hammer and dolly a tank as you can’t get your hand inside, making a Dent Gun or similar the tool of choice.

These work by pulling up on a nail that’s temporally welded to the surface. Done gently, this action teases the dents upwards. First attack the area with a small barrel-sander or die-grinder to remove the tank’s protective coating.

5. The metal is thin, so go extra gently. An experienced operator will know how much is too much. Pulling the dent up too high creates unwanted high spots.

These can be delicately brought down with a carbon-tipped heat-shrinker or some gentle taps with a hammer while supporting the surrounding area with another welded nail.

6. You can bend up some smoothed-off boot springs to get in through the sender or filler hole to help raise up and smooth off any low spots, though internal baffles hinder this approach.

The nails simply snap off and sand smooth when finished. Avoid doing this too often in one area or you will overstress the steel, which can lead to cracking.

7. The best way to get any panel flat is to panel file it. Go easy! The metal is thin so you don’t have much leeway for error. Break through and you can kiss the tank goodbye.

Get it fairly flat before reaching for the file. Then go gently, pulling up any low spots rather than filing the highs — it’s more a guide than a leveller!

8. Wavy sections (as seen at the far right) are typical in metal that has been drawn such a great deal — each tank half is stamped from a flat sheet of steel. If overly deep, the ripples will need to be massaged out.

If they’re subtle, a few heavy coats of high-build epoxy primer or a thin skim of body filler will eliminate them.

9. Time and the elements are adept at seizing exposed bolts, so it’s not uncommon for a few captive nuts, threads or welded-on tabs to be destroyed when removing the tank.

Simply cut some good tabs or threads from a donor tank and weld them to your repaired unit. While plug welding will suffice, a spot welder works a treat.

10. With repairs completed, it’s likely the tank will have a few pinholes or minor leaks. POR’s three-part repair kit (cleaner; metal prep; sealer) is effective at sealing even the most minute amount of porosity.

The sealer is a heavy, aluminium-rich resin that air-cures. Since it doesn’t require a hardener or other catalyst, it’s safe to use.

11. First, the heavy-duty marine cleaner removes rust and fuel deposits. Then the metal prep leaves a zinc phosphate coating and neutralises any remaining rust.

After blocking every orifice, pour in the sealer and rotate the tank until all internal surfaces have been coated. Excess is poured out and should not be reused

12. The sealer must be force-dried with a heat gun as moisture reduces its effectiveness. Leaving it in the sun won’t do.

An LED torch is excellent for looking inside the tank to determine what’s going on. You need to see where the sealer is leaking through and doing its job, so the sealing process must be done prior to painting.

13. Due to the tin/lead finishes on some tanks, apply an epoxy primer like PPG DP40 before applying body filler or high-build primers to finish off the repaired areas.

This will ensure maximum adhesion. From there, it’s the same priming and painting process as for the rest of your streeter’s body work.

14. Final finish depends on the look you’re chasing. The HG into which this tank will be fitted is more a resto-mod rather than a pure resto, so I decided to give it a nice gloss silver top and a gloss black bottom.

If you’re chasing that original look, you could have the tank zinc-dipped after the repairs but before sealing.


Now doesn’t that look better? Although the painting process could be done in a day, you’ll need to let the tank sit for at least four days to allow the resin sealer to completely cure before reinstalling and filling it with fuel.

Note that while POR’s tank sealer works on all metal tanks, it isn’t recommended for plastic tanks.
While you’ve got the tank out, take the opportunity to fit it with a new fuel sender — Rare Spares and VDO have extensive arrays. That will give you many more years of motoring enjoyment.

Many thanks to RLC Engine Reconditioners (07 3390 2017) for the cleaning of the tank; to MPA Paint supplies (07 3822 2300) for supplying the POR kit; and to Streetneat (07 3206 0340).