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Fuel tank rust removal


Adrianb
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No easy way (apart from a new tank, or get somebody to do it for you.

If wanting DIY, drain tank,but do not remove the big drain plug as this is very likely to rip the tube out of the tank. Remove the level sender.

Flush out several times with hose, then add a handful of nuts/bolts or good sharp gravel. Some water and agitate the tank to loosen any rust flakes etc. There are youtube videos of tanks being strapped to cement mixers for this method, saves a lot of effort.

Next part is tricky, you need to flush everything out with the hose again. Once happy, there are a couple of options. I added some phosphoric acid to kill any flash-rusting and give the steel a bit of a coating that hopefully is corrosion resistant. Seems all is good 5 years later. Other options are tank seal kits, like a paint you pour in the tank, move the tank so the entire inside is coated and then leave until fully cured.  Handy if the tank has any weeps/pinholes etc.

Then you are good to go.

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One thing to add to Clive's reply: While there are "tank sealing kits" available, many people (including myself and my local radiator repair specialist) have found that they don't work terribly well. The slightest imperfection in your technique, or the ambient conditions, or just blind luck, results in a skin of varnish that peels off once you start using the tank and blocks the outlet leaving you stranded in the middle of nowhere.

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Hi Adrian,

if it was my tank I would use Bilt Hamber DeOxC.

Blank off all the holes (especially those at the bottom) but leave one at the top open.

A 1 Ltr bottle makes 10 or 20 Ltr of working fluid so you may need 3 or 4 bottles to give a decent level in the tank

Firstly mix 10 Ltr with one bottle and pour this in with the tank in its normal upright position.

Leave for 24 Hrs. This concentrate will attack the rust efficiently.

Then add 10 Ltr of water to the tank and also add the extra bottles mixed at 10 or 20:1 

Lay the tank on its front then back then sides. Leave each position for 24 Hrs.

If possible agitate the mix if you remember.

It will take a week but will be done very nicely.

Drain it out (you can keep it for other jobs) rinse with petrol or simply allow to air dry.

Job done.

 

Roger

 

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I used this kit on my tank in August after finding a hole near the drain plug (which I use as the tank outlet) caused by rusting on the outside. I brazed on a repair first, then used what was left after coating the inside to paint the outside too. It's messy but can't say I'm overly worried about it flaking off.

https://www.frost.co.uk/por15-small-fuel-car-tank-repair-sealer-kit/

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Quoted from Hogie4A-

Hi Adrian,

if it was my tank I would use Bilt Hamber DeOxC.

Blank off all the holes (especially those at the bottom) but leave one at the top open.

A 1 Ltr bottle makes 10 or 20 Ltr of working fluid so you may need 3 or 4 bottles to give a decent level in the tank

Firstly mix 10 Ltr with one bottle and pour this in with the tank in its normal upright position.

Leave for 24 Hrs. This concentrate will attack the rust efficiently.

Then add 10 Ltr of water to the tank and also add the extra bottles mixed at 10 or 20:1 

Lay the tank on its front then back then sides. Leave each position for 24 Hrs.

If possible agitate the mix if you remember.

It will take a week but will be done very nicely.

Drain it out (you can keep it for other jobs) rinse with petrol or simply allow to air dry.

Job done.

 

Roger

 

I'm a fan of Bilt-Hamber products myself; but it cannot be too widely known that their DeOxC is no more than anhydrous citric acid with a fancy label and an inflated price tag. Have a look on fleabay and you can buy exactly the same chemical to use in exactly the same way - it's cheap, safe and readily available - for a lot less money.

 

I think citric acid would do nicely for this job, but I'd be inclined to degrease the tank first. Assuming there's a Screwfix near you, their "no nonsense" degreaser is both cheap and good, I've used it to shift all sorts of stubborn filth.

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  • 1 year later...

Take the tank out handful of light gravel / sand and 3 ltrs derv shake like mad leave shake again shake again for a few hours then go up the pub for a rest come back shake and turn for a few hours .. rinse with water leave to dry … lovely and clean 

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People seem to throw acids at rust without understanding the chemistry.

Any acid will attack rust and convert it into a 'salt' of the acid, eg iron citrate.    But there are "strong" acids, like sulphuric, that are just as  active against the original metal and will erode the structure, potentially damaging  it.   Then there are "weak" acids, usually organics, like citric, acetic, oxalic, or phosphoric acids, which are more active against rust than native iron, so will not damage the part.

The  iron 'salts' are soluble in water, so that once the rust is removed, a bare iron/steel surface is left, which will suffer 'flash rust' almost immediately.     The exception is Iron phosphate which is almost completely insoluble in water, so that a layer of the phosphate is formed and  flash rust cannot happen.   Once dry, the phosphate has a hard, rough surface, ideal as the foundation for paint!

But the disadvantage of phosphoric acid treatment is it will seal a thick rust layer under the phosphate.     Always use a mechanical removal method, and if necessary use another organic acid to dissolve thick rust before treating with Phosphoric.

The cement mixer method was first used, I think by bikers, whose 'teardrop' tanks could be wrapped in an old blanket and put inside the mixer!   

Interesting video from Ed China about this.    He got a load of rust out with just a vacuum cleaner!  Then just dissolved the surface rust, with Evaporust, and mechanically abraded the outside:  

 

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John do you know the cause of the rust in the first place? Theres got to be oxygen obviously and water probably helps but where is all this coming from? I can understand it if the tank is left empty for a long period but if kept full of fuel shouldnt that protect it?

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I raised the question as my tank had been left empty since 1995 and the fuel pipes were fully corroded so I assumed the inside of the tank would have a layer of the stuff over it! But thank you for the updates very interesting.

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I suppose a further question is that if you clean off the rust mechanically will it just come back rapidly, even with the tank in use, because youve lost the surface protection (if there is any used during the original manufacturing process of course)? 

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I'm sure that you are right about Mr.China's tank, left empty for ten years I think he said!    Water does get into the tank, rain when filling, condensed humidity and of course modern alcohol- containing fuel absorbs it from the atmosphere.   Water won't mix with petrol so will go to the bottom of the tank, where it may get sucked into the fuel supply if the vehicle is in frequent use.     But 'our' cars aren't, usually, so some water on there is usual.

A rusted tank may have been painted and/or galvanised in manufacture, but once you get as much rust as seen on Mr.China's tank, none of that is left.    You have to get back to a clean or phosphated surface and apply new paint.

An alternative is the Hammerite route, designed to be applied over the rust, and supposedly seals it in where water and oxygen cannot reach the metal and cause more.    In my experience this is a pious hope!    The tank sealing kits do the same.

Edited by JohnD
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Earlier this week I replaced the sender in the tank of my 13/60, the tank still in place but driven enough to lower the petrol level below where the sender fits.

While the sender was out I thought I would try and look inside to see what the state was.

The matches kept going out* so I had to use a torch, it looked clean but I have no idea if it is the original or not, I think not because even the outside is quite good i.e. not dented, scratched etc.

*Only kidding, even I'm not that stupid (just)

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58 minutes ago, glang said:

Yes its the oxygen thats the big mystery as even a nearly empty tank will be so full of fumes I cant see air getting in - if it did it would be dangerous!

Ah!   You need to consider the Partial Pressures of mixed gases.  A vapour, below it's boiling point, is just one in the mixture, will be present in proportion to its vapour pressure.

The vapour pressure of petrol at room temp is about (petrol is a mixture) 450 mm Mercury (Hg), and atmospheric pressure is 760mmHg.   The rest of the gas inside the tank will be the usual oxygen, nitrogen and water vapour.  

Boil a liquid and it's VP rises to atmospheric (that's why it boils), so all the space above it will be water vapour.   That's why the can collapsed as it cooled back in the school physics lab!

 

Edited by JohnD
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The upper explosive limit for petrol is about 8% by volume.   The atmosphere inside a tank, fully saturated with petrol vapour, is about 60% petrol vapour. Well above explosive.  But I still wouldn't smoke near one!

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10 hours ago, glang said:

 but if kept full of fuel shouldnt that protect it?

Give  me 4* back, more mpg, grow food not 'petrol'.

Modern ethanol (E5, E10, E the future) are all hygroscopic and scavenge water from the atmosphere, therefore, because petrol floats on water the scavenged water gets in the fuel line or makes pin holes in steel petrol tanks. The higher the E number, the more water. A reason why modern car manufacturers offer limited guarantees on fuel systems?

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Taking the point about water and E petrol a bit further, here there is E85 which is being used more and more I assume the car manufacturers are aware of the problem so what steps do they take to counter it? OK, the petrol tank is plastic so no rust but there is still the question of the water being injected into the engine instead of petrol.

I must remember to discuss it with a friend who has had his 3 series BMW set up to run on it, he also has the good taste to own a classic - a 1959 Simca Aronde 

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Ignoring the corrosive potential of water in fuel, water injection is a known 'thing' in engine design.   It can cool and prevent detonation in high compression situations..

A little water, what might occur in regularly used engines, won't be a problem.  At worst,band occasional misfire.      But rarely engines as in classics could accumulate enough to put the fire out.

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Hi,

 Ethanol or E5/E10/E85 does not "suck" water out of the air. It's a myth that will not go away.

Ethanol fortified fuel will enable water that has got into fuel to be safely "burnt" in the fuel & not separate out causing corrosion.

Cheers,

Iain.
 

  

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