trouble cleaning rusty gas tank

Having some trouble cleaning the rusty gas tank on a 77 Newport. I know this is probably the most-discussed topic on the bulletin board but I've searched like crazy and not found the answer. Here's what I did:

Filled the tank with a solution of hot water and phosphoric acid and let it sit overnight.

Emptied that out, then filled it with baking soda-water solutioin and let it sit a few minutes.

Dumped it out, then flushed with water several times.

Dried it with a blow dryer.

The problem is, it re-rusts IMMEDIATELY when I dry it.

Am I doing something wrong? Anybody know how I can prevent it from rusting?

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

Are you using a hose to wash out the tank after you drain out the acid? A garden hose with a "spritzer" thingy is what you need to rinse that tank out. Once you rinse out the baking soda solution, spray some WD-40 inside the tank and a little gas line anti-freeze to remove any residual water. Try to get as much of that liquid out of your tank, even if you have to flip the bike upside down to do it. Once you're all done, fill the tank with your gas/oil pre-mix and keep it filled to prevent it from re-rusting.

Re: trouble cleaning rusty gas tank

So are you saying I don't need to blow-dry it? Is shaking out the water well and spraying with WD-40 and using gas-line antifreeze sufficient to get the water out?

Didn't use the hose before, but I will now...

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

Anything you can do to remove the residual water is better than nothing. Even shooting compressed air into the tank will get some of it out. I always put a capful of gas line antifreeze in the first tank of gas after cleaning it out.

Re: trouble cleaning rusty gas tank

Jason Luther /

any sort of alcohol (gas line anti0freeze) will absorb the water. isopropyl (rubbing alcohol is cheap). when i did mine i just washed the inside out with mineral spirits (not an alcohol, but it still mixed with the water). i like parentheses. but really blow drying is what is rusting the metal. wash it out and fill it with premix right away

Re: trouble cleaning rusty gas tank

type rusty tank in the serch header, you will see that using muriatic acid is the way to go.

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

I've used both Phosphoric and Muriatic acid to clean tanks. Muriatic is a lot cheaper but Phosphoric acid does a better job.

Re: trouble cleaning rusty gas tank

OK, cleaned it again with acid, then baking soda, then the hose, then shook the water out and sprayed it with WD-40. No rust yet, I think I've got it. Thanks for your help guys.

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

Fill that tank with pre-mix and a little gas line anti-freeze ASAP.

Re: trouble cleaning rusty gas tank

I have a rusty tank as well. where do you get phosphoric acid? can you just dilute naval jelly?

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

Behrs Concrete Etcher and Rust Remover in the paint department at Home Depot. Comes in a black plastic gallon jug.

Re: trouble cleaning rusty gas tank

Ok, so if I get this rust remover stuff, how long do I let it sit? Or do I just kinda shake it around a bit and rinse it? It sounds like some pretty potent stuff.

Re: trouble cleaning rusty gas tank

I let mine sit overnight, a few hours would probably do it. The rust reacts with the acid and forms bubbles, so when there are no more bubbles in the tank, you're probably good.

There's an old post from MoPedLar that does a great job of describing the whole process.

Phosphoric acid isn't as nasty as other acids, but you should wear gloves and goggles and stuff. When you're done with it, you can neutralize it with baking soda.

Re: trouble cleaning rusty gas tank

Sounds good. Thanks.

Re: trouble cleaning rusty gas tank

See Ya Moped Army /

Make sure you only use around 8-10 ounces or so and the rest hot water. You don't want to use full strength.

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