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Muriatic Acid for Gas Tank Cleaning

55K views 38 replies 31 participants last post by  drumrooster 
#1 ·
So decided to do it the old fashioned way. Some gas in the tank, nuts & bolts in there for about 15 min, mixing it around. Then the acid about 35% about 1/3 gallon, face shield, overalls, gloves etc. 30 min later after swishing around be very careful, looked good. Dumped it into some water with baking soda to neutralize it. Flushed out the tank with water/baking soda then gas. Force dried with the wife's hair drier. Looked inside, it had turned orangey / rusty when it dried, WTF. Thought I had done it correctly, what did I do wrong.
BTW already tried Rusteco, long story $90 left it for a week, don't think I had enough of it, probably needed $180 worth for my tank, it's a 6T tank I've been told, almost 5 gallons... I wouldn't pay $180 for Blue label far less weak acid..:confused:
 
#2 ·
That orangey rust color that it turned is flash rust, brought on by water and heat from hair dryer, and lack of petroleum product of some kind to coat the fresh and clean surface. It's like when you sandblast metal, it starts to rust almost right before your eyes because it's so clean. If you had dumped a little gas with about a teaspoon of oil in it and swirled it around to cover all sides while it was nearly dry, it wouldn't be so bad. It still isn't that bad, it's just surface rust. You can probably get rid of it with some gas, just don't dump it out until you're ready to use it.
 
#7 ·
If you want to remove rust from metal use Phophoric acid, not muratic.
Phosphoric acid is sold under the brand name "OSPHO".
It is also found in "Naval Jelly", and "Metal Prep".
It turns the Iron Oxide (Rust) into a hardlayer, that can be painted right over.
It is green in color, and when once treated won't rust again.

Dusty,
Orange, TX
 
#9 ·
I just rinsed a super crusty tank in vinegar and it came out super shiny and sexy. I let it sit for about 48 hours and it really did a great job. The other benefit is that vinegar is very easy to dispose of when you're done with it. Its not near as harsh as muriatic acid so it doesn't flash rust quite as fast. I took some pictures of the process and I'll see if I have time to post them sometime today. I soaked it it in vinegar (mild acetic acid), neutralized it, and put it in the oven at about 200 degrees for a while just to make sure it was dry inside so it wouldn't flash rust again. Sounds like one of those urban legends, but it is by far the best thing I've found for it. Muriatic acid tends to work much faster, but flash rusts immediately and is tougher to get rid of when your done.
 
#10 ·
Vinegar works great and you can dump it anywhere when done and it is cheap. I did this to my old Norton tank and it came out clean as a whistle inside. I left the vinegar sit for about 5 days as I kind of forgot about it.
 
#11 · (Edited)
The element in Vinegar is "Acetic Acid". It works, but has it's limits. Another item that works wonders, and is very easy to dispose of is molasses. Mix one part molasses and 9 parts water. Mix it up, say in one of those 5 gal plastic buckets, put in your parts, and let it sit overnight. You won't believe what it did. If it's really rusted (Any Part, Not just tanks) bad, it might take more than overnight. When you are through with it pour down the drain, or feed it to your cows mixed with grain.

For brass and copper fittings. Get the unsweetened Lemon/Lime "Kool Aid". Mix it with water, 4 packs of Kool Aid to a quart of water. Put in glass or plastic container. Drop in your fittings or parts, let sit overnight. Most time all you have to do is rinse off and rub with towel, and it's like new...Well almost. If you google the Molasses thing, I think you will find several articles on using it. Best thing, it's cheap and readily available...

Here is a URL to the Molasses rust removal plus several other methods of cleaning up corroded metal ...

http://www.antiqueautoranch.com/montana500/adrian/rust.html

Here's another site for the Molasses trick...

http://virtualindian.org/projrust.htm

Dusty
Orange, TX
 
#12 ·
I use muriatic acid to get deep rust off. Neutralize and flush. Then a phosphoric acid rinse. I rinse with denatured alcohol to get the "dusty" / "flakey" phosphoric acid residue off.

Also, denatured alcohol is very good at removing gum in tanks - not much will touch it - even acetone seems to have limits working against gum and varnish, but denatured alcohol seems to work pretty well.

I do all my tanks, even new, with phosphoric acid...and don't use sealers.
 
#13 ·
That orange is a very light layer of rust caused by the fact that when you cleaned the metal of heavy rust, you also etched it, which gives it a very large surface area, which will oxidize rapidly.

A couple of solutions:

A conversion coating which converts this minor surface oxidation to zinc phosphate.

Or, "quick prep", a non-rinse metal prep with an alcohol carrier designed for exactly this kind of thing.

You can get either at the autobody supply store.

I'd go with the quick prep. Do not dilute it. The metal will turn from orange to blue and assuming your tank isn't requiring a sealer, put a cup of two-stroke pre-mix in it and slosh it around if you're going to store it.

If the re-rusting is anything more than slight, re-apply the muriatic acid to get rid of it, and then use the quick prep-after rinsing and force drying.

If you're going to use a sealer, you can skip all of this, and simply dump a quart of Por15 in it, slog it around and drain.
 
#16 ·
One last thing - never run a tank after muriatic acid etching without a coating of some sort. ANY water will cause the tank to re-rust. And ALL gasoline has water in it.

POR-15 is a good bet to coat after the flash rust, as the metal will definitely have 'teeth'.

Cosmo
 
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#24 ·
Stuff like molasses and vinegar is great - if the rust isn't bad. But, it's analogous to using a tiny body hammer to pound a railroad spike; that's a job for the BFH.

For heavy rust, muriatic is the ticket. But, as has been mentioned, it WILL flash rust the inside of the tank, and if you let the fumes run rampant in the garage, it can flash rust a whole lot of other stuff... DAMHIK.

I just did a CB750 tank last summer w/ muriatic, and chased it w/ phosphoric. Then sloshed w/ gas. Now, the inside of the fuel tank is the least of the guy's worries!

-Bill
 
#29 ·
I like to use electrolysis to remove heavy scale first. Next I make a rough mixture of pool PH Down (acid in granule form) and water, dissolve it completely, then pour it in the tank. Check on it every hour to see how it's cleaning, dump and refill if you have to and in the end it will be bright silver steel.
 
#32 · (Edited)
Here is another question on this subject.
I used a mild solution of muriatic, worked well.
I want to keep inside from flash rusting.
So I guess now I'm ready for the quik prep acid (phosphoric)
I only have a gallon, the tank is about 3 gal.
Should I just dilute w/ denatured or isopropal?
Calcium,rust,lime remover mixed in?
Vinagar mixed in?
Any other options?

Also the DuPont quik prep is I have is probably 20 years old, does acid lose its effectivity over time?
 
#33 ·
what strength phosphoric acid do you have????........it may already be a weak solution and as such shouldn't be diluted .....if its a high strength it could be diluted as only a weak solution is needed......check interweb net for exact strengths recomended....remember, Coke Cola contains phosphoric Acid and is what cleans pennys when ya leave them soaking in it over night......
 
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