revtothelimit - motorbike forum

I have a fuel tank from which all the petrol evaporated leaving a coating of rust all over the inside of the fuel tank!

I am tempted to try removing it by electrolysis.

I have bought a large bag of soda crystals and plan to fill the tank with a solution of the crystals dissolved in some de-ionised water.
I'd then suspend a fat old mild steel allen key that I found in the top of the tank (without touching the sides) and hook it up with some jump leads to the positive of a fully charged car battery and hook the negative of the battery to the actual fuel tank.
And then leaving it for a few hours....

I'm a little nervous about doing this, has anyone else tried it?
Am I doing the right thing?
Is there a better way?

I've never dabbled with electrolysis, but a solution of citric acid crystals (preferably warm) will get rid of rust very effectively. You will need to stabilise the surface after removing the citric or it will flash rust again fairly quickly. After drying the inside of the tank, a quick mist of ACF50 could be the way forward.

Be aware though, any de-ruster may very well leave the tank doing a passable impersonation of a collander if the rust was too severe...

Mr Mangocrazy’s advice sounds sound.

You could use your soda to neutralise the acid afterwards, before rinsing well with water. Then you’ll feel better about buying the soda.

When I’ve had rusty tanks, I just snipped the gauze off the petrol tap (because it could block with rust sediment) and fitted an inline filter. But I’m lazy.

Petseal was the go to back in my day.

I've used POR-15, worked a treat for sealing a Ducati tank, fixed a pin hole leak too.

Tank sealing compounds often end up as a sticky mess. Safer having the rust.

I've used Petseal and the three step POR-15, the POR-15 was by far the best, left a very clean/metal looking finish inside the tank so it didn't look like it had been sealed. The Petseal was goopy cream coloured stuff, the original didn't play well with high ethanol fuels, I dunno if they've improved it.

I used this on my Ducati tank and then a load of old tools.

https://www.cadetailing.co.uk/products/ ... GIQAvD_BwE

Worked a treat, add powder to hot water, fill tank, shake it for a bit, get bored, go for bike ride, come back a few hours later, drain tank, rust gone. Simples.

Another thumbs-up for POR-15 from me.

I used something similar to crust and a load of old nuts and bolts in an FZ750 tank, it worked but took a lot of shaking.

One of my Z1000J tanks had been lined with some sort of epoxy resin, the tank didn't leak but the resin was slowly dissolving in the petrol and kept blocking the pilot jets, so to sort this out I had the bottom cut out of the tank, the resin removed, it was about 15mm thick in places, the two halves of the tank shot blasted and welded back together. While doing this we found the leak that someone had fix with the resin, so that needed welding as well. The tank was then sprayed and has been very good ever since.

mangocrazy wrote: Thu Oct 02, 2025 5:53 pm I've never dabbled with electrolysis, but a solution of citric acid crystals (preferably warm) will get rid of rust very effectively. You will need to stabilise the surface after removing the citric or it will flash rust again fairly quickly. After drying the inside of the tank, a quick mist of ACF50 could be the way forward.

Be aware though, any de-ruster may very well leave the tank doing a passable impersonation of a collander if the rust was too severe...

This is what i did with the Puch when i got it going after 40 years of being laid up.

Seemed to work ok.

I’ve done a lot of electrolysis on parts but not a fuel tank. It works extremely well. I think you’ll need to apply a sealer afterwards though to stop the rust reforming and to stop any loose bits getting in to your fuel system. The parts I did needed painting or pulling straight away or they start rusting again more or less immediately.

Le_Fromage_Grande wrote: Thu Oct 02, 2025 8:16 pm
One of my Z1000J tanks had been lined with some sort of epoxy resin, the tank didn't leak but the resin was slowly dissolving in the petrol and kept blocking the pilot jets, so to sort this out I had the bottom cut out of the tank, the resin removed, it was about 15mm thick in places, the two halves of the tank shot blasted and welded back together. While doing this we found the leak that someone had fix with the resin, so that needed welding as well. The tank was then sprayed and has been very good ever since.

That’s taking things a bit far, actually fixing it properly!

Deox-c is my goto de-ruster, then por15 to seal

I think Deox-C might be citric acid.

JackyJoll wrote: Fri Oct 03, 2025 5:45 pm I think Deox-C might be citric acid.

I've heard this from a number of sources.

Its either citric or oxalic acid, both white, crystalline and strip rust from metal.
No idea what a kg of citric acid costs?

£5.49 off eBay....


https://www.ebay.co.uk/itm/394806983024

JackyJoll wrote: Fri Oct 03, 2025 11:04 am

Le_Fromage_Grande wrote: Thu Oct 02, 2025 8:16 pm
One of my Z1000J tanks had been lined with some sort of epoxy resin, the tank didn't leak but the resin was slowly dissolving in the petrol and kept blocking the pilot jets, so to sort this out I had the bottom cut out of the tank, the resin removed, it was about 15mm thick in places, the two halves of the tank shot blasted and welded back together. While doing this we found the leak that someone had fix with the resin, so that needed welding as well. The tank was then sprayed and has been very good ever since.

That’s taking things a bit far, actually fixing it properly!

It didn't cost that much, about £300 without the respray - but the tank needed spraying so I'm not counting that as part of the fixing - I had all the panels sprayed, it wasn't cheap, but it does look lovely. 2nd hand Z1000J tanks are currently around £300 and you don't know what you're buying.

De rusting depends on the mess thats inside. I did a tank on a Triumph Speed Triple which had been lovingly dumped in a garden shed for decades, it was so rusty it took me 2 days of WD-40 and gentle persuasion to get the petrol cap open.

First I put a couple of good handfuls of smallish screws in, and some water and washing up liquid in, and shook it round for what felt like a fortnight, to mechanically loosen the worst of it. Then I jet washed the inside thoroughly, and drained and removed the screws. Any stragglers can be fitted out with a magnet on a car aerial type tool.
I did it in the summer, and when fully rinsed, I left it in the sunshine to get good and warm, and rigged up a bathroom extractor fan to sit on where the fuel cap fixes (removed). with the fuel tap etc removed it helped pull out the moisture.

I've tried and tested lots of products to line tanks, if you don't it'll rust up again fast.
There are products that pour in, which contain thinners which evaporate. Few brands tried, none worked well.
I now stock and use Flowliner - it's a 2 pack epoxy type, add the hardener, then make sure the inside is well coated. Found it better to get the top done first while there's plenty of gloop (technical term) to move around. You have to keep the tank moving so it doesn't well up, it could split the seams of the tank. I use an old tyre, to sit the tank in, and move it around every minute or so, just small movements so it runs, not drips, as to evenly coat the whole inside.
I'll try and post some pictures up later.
Flowliner £42.72.