[AJD] Phosporic acid and cleaning a gas tank

Steve Treimer steelerhawk at yahoo.com
Mon Jul 18 07:08:31 PDT 2005


Kyle,
As an experiment, you could try sticking a nail in a glass full of Coca-Cola or Pepsi.  Both are formulated with phosphoric acid to give the pop it's acidity.  If I remember correctly, the nail will rust and get eaten away.  
While iron will react with phosphate to produce the protective iron phosphate coating you're looking for, the strong acid will similarly cause the metal to rust.  I'm not entirely sure now the iron phosphate treatment products work, but I'm not surprised that you couldn't get a rust proof coating.  having pre-treated with muriatic acid may be why, but since you thoroughly rinse, I'm not really sure.
Like Eric, I used Kreem on one of my gas tank after a similar cleaning such as yours.  The rust that you see in your tank would only be surface and should come right off with a blasting of water and rinse with several subsequent washings of isopropyl alchohol and/or acetone.  Then coat with the Kreem and you should be golden.
Don't get discouraged!  You're definitely on the right track.
Steve

Kyle Sands <willys_46 at mail.com> wrote:
I would never have imagined it would be so difficult to find phosphoric acid. I called all over town asking for it by name and also under names such as ospho, metal prep, or metal etch. Nobody had anything, but more likely, I don't think anybody had a clue what I was aksing for...

In desparation, I went to a fleet store and looked through all their cleaning products to see what I could find. I finally found a product called rust destroyer or something like that and it listed the active ingredient as phosphoric acid. It cost my 8 bucks for 32 oz. but I didn't care.

I had cleaned out my gas tank using muriatic acid to eat away all (or at least most) of the rust inside. I then washed that solution out with a lot of water and poured in this rust destroyer stuff. I sloshed it around, let it sit, sloshed it around again, let it sit, and did that several times leaving it in overnight. I poured it out the next day figuring my tank was ready - sealed and protected from future rust.

Wrong! I opened it up a couple days later and rust is starting to form on the walls and on the little metal dipstick. What's going on? I thought phosphoric acid was supposed to coat the metal with a protective coating?? Am I wrong, or did I mess up somewhere?????

Kyle Sands <>< Alexandria, MN

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