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MG MGA - Cleaning the gas tank

I rocked the gas tank back and forth (this project car has been apart for 15+ years) and it sounds like sand is in there. I know it's rust. The outside is pretty clean looking. No major dents, pitting, holes, etc.

It'd like to determine whether it's worth saving.

How best to test it?

How best to clean/seal it?


Phosphoric acid will dissolve and neutralise the rust. Seal up all the orifices and spin it round for as long as you can. Look for pinholes. Flush with water, then dry quickly with compressed air or out in the sun. Coat the interior with a proprietary compound.
Dave H
Dave Hill

Ah.... I knew that, long forgotten. Thanks.

I had a response on another forum... strap it to a home cement mixer with a handful of gravel in it.

If I do that, (yea, right) I'll post a video.


I wouldn't use gravel either, but there is a method to that madness... The kit I used to etch and seal a rusted ATV tank years ago included a short length of chain. This was placed inside the tank with the acid etch, and when the tank was sloshed with the acid, the purpose of the chain was to dislodge any loose bits of rust.

D Rawlins

As for sealing the tank after, I have had very good result with the Bill Hirsch tank sealer, that is impervious to alcohol fuel (but not MEK). It sloshes around and seals the metal and will fill small pinholes as well. Forms a very thin coating. I would use the phosphoric acid as apposed to other mechanical means as the original tank has a lot of baffling in it, and the rocks, screws, chains, etc. may not get to all the places needed.
C.R. Tyrell

If I'm not mistaken, phosphoric acid forms iron phosphate which is insoluble and stops further action. Good rust stopper but not good at dissolving it all.
Some of the organic acids are better, as in radiator cleaners.
Art Pearse

Careful with the Hirsch product.I used it for years in my MG,boats,tractors and motorcycles with good Illinois alcohol fuel. Took my boat to Florida,came home with almost a full tank and 4 months later found what looked like a plastic bag floating in the tank.Tractors sit for 6 months here with no trouble.Something in that central Florida gas didn't get along with it.

gary starr

I was faced with a similar repair or buy new decision several years ago; I chose a new tank. I'd heard too many horror stories about the various gas tank sloshing compounds and their high failure rates. If there's even one spot that's not cleaned properly and the sealant fails to adhere properly, you'll have issues sooner or later.
Nick Kopernik

Chemical dip, leave it bare inside. That's the only way I do it anymore. I just had another one done recently, this time off a 70 year old tractor. It looked like something you would throw away beforehand, but after the dip looked brand new inside and out.

Gravel is actually an excellent way to clean a tank, but not one with baffles. It's typically used to clean air and water tanks.
Steve Simmons

This thread was discussed between 03/09/2015 and 04/09/2015

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