Gas Tank Rust

[Julio A.]

I had a lot of small pin holes before in my tank caused by rust eating too much of the tank. I had it split open, thoroughly cleaned and patched and re-welded again and sealed the seams by brazing copper. It was then leak tested using water. The thing passed with flying colors. After fixing my petcock and re filling the tank, I noticed a slight pin hole leak under my tank, just after the welded seam. No big problem though, already patched that up permanently with steel epoxy, it was under the tank anyway. After 24 hours of letting the epoxy cure, when I inspected the tank, it was as rusty like before. Apparently, the epoxy liner I used got dissolved by gasoline.

POR15 is definitely unavailable here and with the prices they sell Kreem here, I might as well buy a new tank. I'm racking my mind like hell on what to do now. I'm thinking of using rust converter in the tank and promptly re-line the thing with something more resistant to gas. What to line it with is the problem.  

[Bob_Roller]

I've removed heavy rust on two fuel tanks in the last few years, I used POR15 .

The process I used, was to fill the fuel tank with plain old white vinegar let it sit for a week or two, drain it rinse it out with water then put phosphoric acid in there and shook the tank around a bit, rinsed it out dried it out with the exhaust from a shop wet / dry vacuum cleaner .

Then put the sealer in .

If all you have available to you, is KREEM, don't have much choice but to use it .

As with painting, surface preparation is the most critical step for lining a tank .

[Luca]

What's the cure time on your epoxy?  I know that the POR product (it's technically not por-15) instructions say to let the tank sit for 4 days before refilling with fuel.  Keep in mind that anything that dissolves in the gasoline will make its way to the carburetors.

Was your epoxy patch rated as a gasoline-proof product?  As far as lining goes, you really need to use a gasoline tank liner product -- Kreem, POR, or something else available to you.  It is expensive, but when done right it works.  Alternatively you could not line the tank at all and clean it out yearly with dry alcohol and etchant.  The mighty Snowbum does not line his tanks!

After you tested the tank for leaks with water, did you flush it out with a dry alcohol and use some sort of etchant to get rid of the flash rust?  If not you will have kickstarted the whole rust/rot cycle again.

The reason it passed with water but leaked with gasoline is because gasoline is much thinner than water.
Keep in mind that any used tank you get will be subject to the same problems you are having with yours now.