How Do I Repair My Fuel Tank?

If you need to rescue a rare fuel tank, avoid lethal welding or the cost of a new tank, try to repair your tank at home!

Internal fuel tank corrosion particularly affects cars left standing for long periods of time. Condensation and the corrosive qualities of fuel gnaw away at steel fuel tanks. This results in flakes of rust being washed from the walls of the tank by the fuel itself, drop to the bottom of the tank, accumulate and get sucked into fuel lines and filters. Externally, all might appear fine. Lack of fuel is the first warning sign and time to take action. Far worse is a never-drying patch of weeping fuel on the outside of the tank, perhaps from a seam or simply on a sidewall. At this stage, alarm bells should be ringing. Leaking fuel is a deadly dangerous big deal.
Forget fuel tank welding. There are specialists who can do it but it’s NOT a DIY prospect. Petrol vapours inside a dry fuel tank can still ignite long after the petrol has gone. A new tank is perfect – if one is available. Enquire as to whether it has an internal protective coating, though.

SKILLS: Competent
TIME: One day plus drying times
COST: £45-£70

Frost’s 4-stage Fuel Tank Repair Kit is perfect for sealing weeping seams and halting internal corrosion.

1. Remove internal fittings such as a fuel gauge sender unit. Note the rusty sludge in this Peerless’ fuel tank with old fuel residue. Expect this if your classic has stood for a number of years or if you leave a minimum amount of fuel in the tank for long lengths of time.

2. Gloves on, I chose to strip the paint from the outside first. Once done, rinsing the paint stripper off could be done at the same time as the first internal rinse

3. Once stripped, wipe off any excess paint stripper. Inspect carefully for pinholes and rust.

4. These loose crumbles came from the other tank, which was dry inside. Remove loose debris if possible.

5. Tape up any holes, leaving the filler neck open for now. I used masking tape. Gaffer tape’s superior adhesion is ideal.

6. Wearing gloves and using a container, mix the Cleaner Degreaser (Marine Clean) from the kit 1:1 with very hot water and pour carefully into the fuel tank using a funnel.

7. Seal filler neck hole. Shake the fuel tank vigorously, turning at the same time to allow the solution to clean thoroughly. I left the mixture in for 20 minutes*. Shake vigorously again. Remove solution.

* Depends on the job that you might have to wait for a bit longer. Baked-on oil may take up to 2 hours of soaking before it can be easily brushed or sponged off; gum and varnish in a gas tank may take 24 hours or more. Hot solution works better.

8. I poured it back into the mixing tin. It looked like filtered coffee remains from a cafetiere. Imagine that in your car’s fuel system! That’s come from years of rust flakes, fuel gum, fuel varnish and general debris.

9. Rinse the tank thoroughly using a hose, until the water runs clear. This was my result. Pretty impressive compared to pic in step 1. Now the exposed, totally clean metal can be treated with Metal Prep (was Prep & Ready) rust remover based on phosphoric acid. This goes in neat.

10. Seal the filler neck. Agitate regularly. Leave Metal Prep in for a minimum of 30 mins. Overnight is best though. Rinse thoroughly until the water runs clear. Drain the tank.

11. A low centre of gravity via the tanks helps the Peerless handle. Full of fuel and sited in the sills, I could see the logic. I pray I’m never T-boned in it, though. A sobering thought.

12. Now dry the inside of the tank using an air compressor or a reverse-action vacuum cleaner as I did. Vacuum cleaner air is warm and dried the inside in 10-15 mins. The inside must be absolutely dry for the next stage. This is VITAL.

13. Block all holes again, bar the filler neck with fresh tape. Pour Tank Sealer carefully into the tank using a funnel. Tape over the hole. Tank Sealer requires full skin protection. Trust me on this: you must wear gloves. I wore ones that split. NOTHING I tried removed the small amount of sealer from my hands. Three days later it was just possible to scrub it off with a scouring pad.

14. Gently rotate the tank, allowing the sealer to coat all nooks and crannies, baffles and so on. I left each tank to stand for ten minutes, then repeated this step. Drain unused solution for 30 minutes to avoid puddling the sealer. I then left the tanks alone, tape off, for four days, lying flat to dry completely.

15. First, I sprayed Metal Prep on to the bare tank outer, left it for 30 minutes and wiped dry. I’m a big fan of etch primer and used Etchweld for its long-lasting adhesive capabilities.

16. Just one 500ml can covered both tanks. You might prefer a brush-on primer and topcoat. Either way, don’t buy inferior primer.

17. Using an acrylic black gloss topcoat, the tanks now look the business. Nearly 50 years on, the original fuel tanks have been saved, for at least a quarter of the cost of a single refabricated version.

18. Trial fitting and another Peerless hurdle overcome. The fuel delivery on a Peerless did not have twin fuel filters fitted between the twin tanks and their fuel pumps. I shall be fitting said filters. After a blocked fuel line on my Spitfire due to fuel tank debris, an inline fuel filter was fitted to protect the fuel pump.

19. Part four of the Frost kit is a fuel storage additive and stabiliser. It stops the gum and varnish, as shown on this sender unit, from forming and maintains fuel octane levels. All products in the kit are available individually from Frost. Cleaner Degreaser is ideal as an industrial cleaner. Metal Prep is ideal for bare steel use.

20. I like new products that do exactly what I’m told they do. Rust Buster (again from Frost) came to my aid while I was trying to undo sender unit screws to no avail. All the screw head slots were becoming enlarged, so reaching for WD40, which I used on three of the screws, I thought a comparison was in order. Rustbuster was at least twice as fastacting as WD40. In fact, I ended up using it on top of the WD40’d screws because the delay was holding up our workshop photos. Can’t say fairer than that. And it’s safe to use. Grand.

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