Gas Tank Rust - Phosphoric Acid vs Evapo-Rust?

[Chuck78]

I got a good looking tank from WittTom last year to replace my deer-dented tank. Paint looks nice but I noticed a fair dusting of rust specs inside. Nothing terrible, but heavier dusting in the bottom as I saw from the petcock opening. I ran about 1/4 gallon of gas into it, closed it, & sloshed it around substantially, & drained. Repeated 3 times. The gas goes in clear & comes out tan/gold tinted every time. Time for some rust removal...

Seems to me that the non-toxic Evapo-Rust product works wonders in 24-48 hours, & can be had at advance auto, O'Reilly, & Wal-Mart.

Phosphoric Acid has long been a great agent to clean rust as well, but is a bit on the hazardous side, & I don't know how it will affect paint. It can be neutralized with a few teaspoons of baking soda in a gallon of hot water afterwards. It seems that the phosphoric acid will act much quicker to remove the rust. In the bottom if the tank I am a bit more concerned about the extent of the rust. Petcock is removed, blank off plate made from 1/8" steel bar stock.

Muriatic Acid (Hydrochloric Acid) is also used frequently, but is much more harsh, has dangerous fumes, & is very harmful to your skin & eyes,but makes the tnk shine like brand new metal in a very short time. Baking soda wash with hot water neutralizes it also. "Acid Magic" is a "safe" form of muriatic acid to use, but seems harder to come by. No fumes, less harmful.


Any tips or opinions on using either of these products? Is it critical to use purple power or some other detergent or degreaser beforehand? Will Acetone suffice for that? Or something water based? I have read that it will help speed up the process

[trtsmb]

When I did my tank a few years ago, I poured a couple gallons of white vinegar in, tossed a piece of chain in (not so heavy that it would dent the tank) and then agitated the whole thing every few hours over the course of about a week. It is a slow method but the inside of my tank was sparkling when I was done and the chain was a lot easier to fish out than a bunch of ball bearings.

[BADJACKSON]

I like the chain idea!

[portdave]

I just did mine with apple cider vinegar. Filled the whole thing up and just let it sit in there for about 5 days. Amazing how much surface rust came off. I should have taken a picture. Easy to work with and I did not put anything inside. You can also strain it when done and use it again.

[trtsmb]

Mine had been sitting for over 5 years so the chain was a little extra.

[Nessism]

There are various method as demonstrated in this thread already. Most professional shops use phosphoric acid. Home Depot sells Metal Prep for about $15/gallon which will eat that rust out in just a couple hours or less. Drain well and save for reuse. Rinse with water and done. No need to neutralize. The metal will be lightly coated with a passive coating afterwards which helps retards flash rust. I'd hit the tank with WD-40 right after rinsing though otherwise you will see some red form. EvaopRust also works nicely, particularly if you have paint you are trying to protect. It's more expensive but safer.

[azr]

Ed, does Home depot call it Metal prep, or something else?

[Chuck78]

KleanStrip brand Phosphoric Prep & Etch:

http://www.homedepot.com/p/Klean-Strip-1-gal-Phosphoric-Prep-and-Etch-GKPA30220/100406369

Basically the same thing as the Behr Concrete Etch & Stain Remover, the Klean Strip says for cleaning metal & concrete, prepping metal for paint, & removing iron oxide stains

[Chuck78]

The KleanStrip is $6/cheaper per gallon

I tried the vinegar method, & found it not nearly as aggressive, takes many days to get surface rust off, & not good at pitted rust removal. Apple Cider Vinegar in the strongest concentration I could find, which was still quite dilute. The ACV method also was much more prone to immediate surface rusting. It seems as if Evapo-Rust is the best all around, & Phosphoric is the quickest deep clean possible but requires more care around good painted surfaces, your skin, & eyes. Muriatic/Hydrochloric Acid is the absolute most effective (buy as muriatic acid for masonry cleaning or pool chemicals), but unless you get the less toxic form branded as Acid Magic I think it was, this is the most dangerous and produces bad fumes. The Works toilet bowl cleaner also has lots of Hydrochloric Acid & is very popular to use for this, & very very cheap.

Any further thoughts on degreasing the 36 years of gas varnish & dried up gum before trying to de-rust the tank? I read one source that said the acid won't cut through that stuff well, that a hot water detergent or degreaser solution is what you need. Thoughts/comments?

Trying to get my bike on the road for a big event here this weekend at the Rice Paddy, http://www.RicePaddy.com , the awesome vintage Japanese bike salvage & parts yard here in Columbus, OH for 3rd annual http://www.pinnedohio.com event this Saturday. Lots of chopper builders & vintage bike fanatics, bands vendors entertainment & lots of bike talk amongst a few hundred people.

[Nessism]

Yes on removing the varnish before derusting. I think hot water and some sort of detergent should do it. Some guys use PineSol to clean carbs, so that stuff may be a good choice.

Oh and yes on the Kleen Strip Etch and Prep

[azr]

Right, I remember now, we can't get Phosphoris acid in Canada best we have is Vinegar.......

[RedBaron]

Over the years I've used vinegar, phosphoric acid (kleen strip), and evaporust on a few different machines. Vinegar is cheap and convenient, but does flash rust quickly. Phosphoric acid works well but I have to drive ~40 minutes to get it, and I've saw it rust too (I think in areas that were previously rust free so no protective layer could form). Evaporust requires zero thought to use, but is outrageously expensive compared to the other options. It's also slower to work than the other two options and seems to take much much longer on severe rust (seat pans and such). It didn't harm paint when I'd used it, while vinegar and phosphoric acid has removed paint in sheets (useful just for that at times). I keep all 3 of the above chemicals around and they're all useful. I do like the evaporust in lightly rusted tanks because it's really simple to use, but purchasing a volume capable of cleaning an entire tank is expensive, even when the tank is tilted different ways to get each inside area in turn. I don't know about fuel residue as I haven't dealt with it too bad on my old stuff. Perhaps a liquid engine decarbonizer? I know one that works well to clean carburetors, but it's also aerosol based and super expensive (mercury powertune, emptied into a cup for cleaning). All of the liquid engine decarbonizers I've used don't work as well on fuel gunk (Stihl, Yamaha ring free, etc.). I think Nessism has the better idea using hot water and detergent of some sort.

[BADJACKSON]

I'd like to know how to scrub the inside of the tank.

[Chuck78]

http://www.acehardware.com/product/index.jsp?productId=3607507

Well geez... @ $9.99 a gallon & available from some Ace Hardware stores, Certol's Acid Magic "muriatic acid replacement, 90% as strong and no dangerous fumes or harm to skin" may be the best thing to use! I read a review of a guy that says this is basically all they will ever use in their shop to clean rusty tanks.

[AdamW]

I've tried Metal Rescue, Vinegar, but nothing compared to Evapo-rust for great results. If the rust is not too bad, put it back in the container to use for another project. Cost is the only downside to this.
-Adam