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How-To Restore Your Classic’S Fuel Tank

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#1 Frost Auto

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Posted 02 January 2017 - 08:55 AM



Remove, flush, seal and future-proof your fuel tank at home



Classic fuel tanks can rust readily. This quite often happens from the inside out, so you might know nothing about it until external symptoms start to manifest themselves. Petrol leaks are the most extreme example, signifying that the corrosion has completely penetrated the tank’s structure. A long time before this happens, though, the petrol will start to be contaminated with rust particles. Larger particles will block fuel filters; smaller particles may find their way into the carburettor and clog jets. If you find either, the tank is the most likely source.




The problem is exacerbated by leaving a classic standing for long periods of time. Modern petrol doesn’t help, either, as the ethanol it contains absorbs water during long term storage and speeds up corrosion.

Of course, you don’t have to wait until symptoms appear before you take action. If caught early enough, it’s possible to use a specialised sealer to reclaim a rusty tank and avoid the expense of replacement or refabrication. Simply stripping the inside of the tank will initially cure the problem – but it won’t prevent rust from coming back. For complete future-proofing, it needs to be treated with a tank sealer.
Sealers have a mixed reputation as early versions proved to be incompatible with modern petrol. The latest POR 15 system from the USA, however, is a safe bet. American fuel has far higher levels of ethanol than ours, so it should resist anything supplied on UK forecourts for the foreseeable future. Kits like the one we’re using in this feature are available in various sizes from Frost from £42.49 including VAT (01706 658619, www.frost.co.uk). Removing the tank provides a good opportunity to replace dodgy fuel lines, filler and breather pipes, filters and tank seals. Remember to clear any rusty silt out of the fuel line before you connect it back up.



1. Clean outside


Tanks located under the car have a hard life. Give the exterior a preliminary clean and degrease. Wait until absolutely all fuel traces are removed (see step 6) before using a wire brush or a scraper.



2. Remove fuel sender


Senders are usually attached with a circle of screws or a locking ring. If it’s the latter, a good dose of penetrating oil will usually be needed to release it. Fit a new rubber seal on reassembly.



3. Apply duct tape


Seal all the tank’s orifices except the filler with duct tape, including fuel gauge sender aperture and fuel pipe connections. Ensure the tape is firmly stuck down to avoid leakage in the following steps.



4. Add degreaser

The POR 15 kit includes a degreaser that removes all traces of old fuel and gunge from the inside of the tank. Dilute it 1:1 with warm water and pour it in. Seal the filler neck with more duct tape.
5. Shake vigorously
Turn and shake the tank vigorously so the degreaser coats all surfaces. Keep doing this at regular intervals for at least half an hour. Drain and repeat with fresh degreaser until it comes out clear.
6. Rinse out
Remove all the duct tape. Rinse out the tank several times with a hosepipe to remove all traces of degreaser from the inside and outside. Be thorough. Drain as much water out as you can afterwards.
7. Add rust remover


Seal the tank again with duct tape. Add the POR 15 Metal Prep solution without diluting. It contains phosphoric acid, so wear safety glasses and gloves. Wash splashes off your skin with cold water.
9. External rust removal


Paint the tank exterior with the Metal Prep solution you just drained out. Leave it for an hour or so, then apply some more. Do this several times. Work it well into any rusty areas with the brush.



10. Rinse and dry


Rinse the tank thoroughly inside and out. Try to drain as much water out as possible. It now needs to dry completely. Leave it in the sun or near a heater for a day-or-two, turning it regularly.



11. Add tank sealer


Reseal the tank apertures with duct tape and pour the POR 15 Tank Sealer through the filler neck. Seal the filler neck. Follow the provided instructions to calculate the quantity of Tank Sealer to use.
13. Paint exterior


Now’s an ideal time to paint the outside of the tank. Chassis paint brushes on nicely and provides a suitably thick and resilient coating. Fit the fuel gauge sender and the fuel pickup (if present).
Removal and Refitting Tips

1. Draining


Drain the fuel into a suitable container via the drain plug or fuel outlet – or syphon it out through the filler neck or fuel gauge sender orifice. Dispose of the old fuel safely or save it for cleaning purposes.
2. Removal
Remove the fuel gauge wiring, fuel pipe(s), filler neck pipe and any ventilation pipes. Most tanks are secured by steel straps or bolted directly to the body. Undo the fixings and lift or lower the tank out.
3. Refitting
Reconnect the wiring. Replace any imperfect pipes and reconnect. Use new hose clips. Fit the drain plug with a new washer. Pour in a can of fresh petrol using a filter funnel. Check carefully for leaks.
What You Need:
- POR15 Cleaner Degreaser (was Marine Clean)
- POR15 Metal Prep (was Prep and Ready)
- Or you can buy a complete Fuel Tank Repair Kit which includes all three steps that you need , depends on the size of your tank.


#2 carbon


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Posted 02 January 2017 - 11:57 AM

For anyone planning to use tank sealer for an early Mini petrol tank, please note the 'Tech Tip'


Tech Tip: fuel pickups often have a gauze filter. Clean thoroughly or replace.


Gauze filters have been fitted to most of the standard Mini petrol tanks I have worked on, these are up to mid-70's examples, not sure about later ones.


I've also has these in-tank filters block up without using tank sealer, and they are a devil to clear. Trying to blow clear with full airline pressure made no difference, ended up using another petrol tank.

#3 Alice Dooper

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Posted 02 January 2017 - 12:32 PM

I love POR15. Though it's not the easiest of stuff to work with, likes to run and the surface needs to be really clean.

#4 minstix


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Posted 11 May 2020 - 08:00 PM

Has anyone tried using Tank Sealer in a classic mini petrol tank? Doesn't it permanently block the gauze filter that's on the inside end of the pickup outlet pipe?


I'm restoring my two original petrol tanks from a 1969 cooper S.

#5 henryS


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Posted 16 November 2020 - 05:43 PM

Yes, doesn't the gauze filter get coated and block the outlet? I have a'73 tank and theres a gauze filter - would like to know how on earth you can get to this to replace/clean it!

#6 timmy850


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Posted 24 November 2020 - 11:20 AM

Remove the internal filer and put an external pre-filter in before the pump?

#7 henryS


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Posted 24 November 2020 - 01:32 PM

Thanks. I did wonder this. Is there any easy way to get the gauze filter out without cutting the tank open haha


#8 GraemeC


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Posted 24 November 2020 - 01:36 PM

To remove it, poke something up the outlet pipe and knock it off - you'll not get it back on though


To keep it clear whilst using tank sealer, maybe you could blow low pressure air up the outlet pipe until the sealer has gone off?

#9 henryS


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Posted 24 November 2020 - 02:03 PM

Thanks, if it’s as easy as that I’ll give it a go :)

I was going to use the Frost tank kit to re-seal it.

#10 Tornado99


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Posted 24 November 2020 - 07:35 PM

Saw a video on a mini tank that had a fuel pickup clogged from a sealer. The guy used a speedo drive cable to poke into the pickup line and with a power drill turning the cable, was able to clear it successfully.

Do be careful with tank sealers. Lots of horror stories on classic bike forums with sealers separating off inside of tank or sometimes turning into a goo with fuel eating it, presumably from ethanol.
Some buyers will not touch a tank or bike if it has been sealed.

Edited by Tornado99, 24 November 2020 - 07:36 PM.

#11 henryS


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Posted 24 November 2020 - 08:16 PM

Thanks for the advice, managed to remove the gauze so will follow the Frost / POR15 instructions carefully!

#12 Tornado99


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Posted 24 November 2020 - 08:52 PM

Here's the viddy I mentioned:


#13 Tornado99


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Posted 25 November 2020 - 06:51 PM

For those not using sealers, there are some tips for keeping things preserved during winter storage.

If you can, drain the tank fully (also good to drain carb float bowls) as fuel will leave a nasty precipitate behind if a puddle is allowed to evaporate over time. Very hard to remove that stuff. I like to spray in wd40 or similar to an empty/dry tank when possible to help protect inner metal. No issues when filling up later.

Best to keep tank near full if not draining it completely. This reduces the air space above the fuel, less moisture there for condensation to appear from.
If possible keep in an enclosed space with a temp higher than outside. Only needs a slightly warmer temp, again this reduces airborne condensation settling on colder car surfaces.

Add some fuel stabilizer. This stuff traps moisture in the fuel and keeps it from forming a separate layer at bottom of tank, causing issues at next start up.

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