Reasonably successful tank cleaning

The Columbia tank had a good coating of rust inside, and I decided to do the acid cleaning thing. Here's what I did, and how it went:

Removed the petcock, and rigged up a tube for the tank fitting. Clamped off the tube with a hemostat. My first error was neglecting to soak the tank with paint thinner first, more on this later. I filled up the tank with full-strength muriatic acid ($1.79 a gallon) and let it work.

My second error was slightly overfilling the tank with acid. As it worked, the gas produced caused the tank to burp occasionally, which was slopping drops of acid onto the frame and motor. Used a turkey baster to lower the level, and it was fine after that.

The acid worked hard for a couple hours, and then slowed down. Drained it off and what I could see of the tank was totally spotless - nice. Flushed with water from the hose for about 10 minutes, and drained it all off again.

When you clean a tank with muriatic acid, you really should finish off with a phosphoric soak, to condition the metal and prevent almost immediate re-rusting. I'd tried about 3 places, and there was no phosphoric acid to be found. So, I did the next best thing - I dumped 3 liters or so of coca-cola into the tank, and let it work. And work it did - fizzed and sizzled away in there almost as hard as the muriatic did.. coke is nasty stuff.

Half an hour later, I drained the coke, drank it (kidding), and flushed again with water.

Now came the denatured alcohol to dry up any water. Filled the tank and let it sit for about 15 minutes, then drained and saved the alcohol. Here's when I discovered my first mistake - the alcohol came out yellow. There was dried up varnish in the bottom of the tank, and the alcohol was disolving it. I should have soaked it with thinner first. Put some more alcohol back in, and let it soak for an hour. Drained this off (it was yellow-brown).

Reinstalled the petcock, and filled with fuel. Fuel took a slight yellow tint from the remaing varnish in the tank. Hopefully it will burn OK, and I don't have to dump it - that synthetic oil is too pricey to waste.

One thing I noticed, is that the columbia has a pretty small tank capacity. Don't think I got much more than 0.7 or 0.8 gallons of anything in or out of that tank.

Hope some of this is useful info. Comments always welcome.

Re: Reasonably successful tank cleaning

I think I found phosphoric acid in one of the rust removal products sold under the naval jelly brand. It was in a spray-bottle (like windex bottle, not arosol) and around 8 ounces.

it was really thick and pink.

I diluted it with water and plugged the tank fitting with a piece of wood.

I remmber that it got pretty hot.

It left the tank on my o'l kinetic pretty clean.

Coke would have been cheaper, and a better story tho!

Re: Reasonably successful tank cleaning

I was out of luck on the phosphoric.. every place I asked for it, I got blank stares.

The muriatic was cheap, and did all the hard work.. Coke was just for conditioning.. one nice thing about it, is that with all the carbonation, it's kind of self-agitating.

It left a darker tint on the metal, so I assume it did something useful. Time will tell.

Wonder if the muriatic can be re-used several times? I'd tend to think so.

Re: Reasonably successful tank cleaning

try it, and see if it reacts.

did the alcool cost a lot?

also, to remove the water, can't you simply put some gaz in the tank and shake the tank?


Re: Reasonably successful tank cleaning

the alcohol helps the water evaporate. Gas and water don't mix so well.

I also let the muriatic acid do most of the work.

the only way I found phosphoric acid was by reading the active ingredients on the back of all those rust removal products.

Re: Reasonably successful tank cleaning

Yes, the alcohol cost too much.. $8.95 a gallon. I can reuse it as solvent, or to dry a few more tanks, but I wish there was a cheaper method. I"m sure there is, but I do not know if it.

I don't think that products like paint thinner will absorb water the way alcohol does. And stuff like WD-40 etc just drive water from the surface, without actually absorbing it.

Re: Reasonably successful tank cleaning

Phosphoric Acid is available at Home Depot as Bahr's concrete cleaner, in their paint dept.

Re: Reasonably successful tank cleaning

if you removed varnish from the tank, wouldnt that mean you should put it back also? is there a reason for it?

Re: Reasonably successful tank cleaning


In this case, the "varnish" is dried up, old gasoline residue.

Re: Reasonably successful tank cleaning

oooooh gotcha :p

Re: Reasonably successful tank cleaning

anyone ever tried CLR in their tank?

Re: Reasonably successful tank cleaning

That is an excellent story. Have you heard of POR15. Check out their website.

Re: Reasonably successful tank cleaning

I'm going to try this myself... so paint thinner - let it work for an hour or so? Then Muriatic Acid for a few hours, then coke for like an hour? Can I refill with the original gas? If not how do you dispose of the gas, paint thinner, and acid? That sounds like a toxic pain for my driveway...

Re: Reasonably successful tank cleaning

steve meyers /

My 2 cents - NON CHEMICAL WAY.

I had a tank that was sitting for 8 years with gas.

1. Removed tank and petcock and cap.

2. Drain tank into a containter (take container to WASTE RECYCLER)

3. Power washed inside of tank

4. Dry tank with air compressor.

5. Seal drainhole with duct tape

6. Fill gastank 1/4 with a mixture of small sharp stones, aquarium gravel, BBs, broken glass, ect..

7. Duct tape over gas cap hole

8. Duct tape a thick towel around the gas tank.


9. Make sure your wife isnt home.

10. Stick tank in the dryer - NO HEAT - for an 50 minutes.

11. You may need to repeat steps 9 and 10 a few times.

12. You can also take it to a commerical laundrymat if you have a larger tank.

My tank was clean and shiny

For those of you that have a tank/frame - I pulled my tank/frame behind a boat for an hour with life jackets attached to it and a long rope. It came out great with no damage and the frame was really clean

Re: Reasonably successful tank cleaning

steve meyers /

oops... I forgot...

Remover tank from dryer and dump everything out of the tank and rinse with water until everything is out and dry with compressor.


Re: Reasonably successful tank cleaning

i just tried this method today...

i couldnt find any phosphoric acid either so i used coke too.

after the muratic acid wash i could no longer see any rust in the tank. BUT, after the final denatured alcohol rince i looked down and saw my takn was coated with rust again!

i filled her up with gas again and she seems to be running fine but that is how rust in the tank seems to be: fine one min and not the next.

should i do it all over again when i can find some phosphoric acid? or is there something else i can use after the muratic acid that will coat my tank so it wont re-rust? i have heard of the Kreem thing. maybe a combination will be ok?

Re: Reasonably successful tank cleaning

What do you guys do with all those chemicals?

Re: Reasonably successful tank cleaning

Steve, I like your style. If there was an award for "Most Creative Use of Tools", you'd win hands-down. I mean, using a ski boat? For moped repair!? CRAAAZY!

Re: Reasonably successful tank cleaning

you have to contact your local hazardous waste recycling/disposal place. there is one about 20 min from where i live where i have to take all my rust contaminated gas. otherwise, may of the chemicals can be put back in the container and used again.

Re: Reasonably successful tank cleaning

steve meyers /

Actually it was an old bass boat. But it worked.

I personally like the tank in the dryer trick.

Re: Reasonably successful tank cleaning

The Muriac acid actually causes your tank to rust. You can buy phosphoric acid as rust remover/metal conditioner at an autoparts store.

Re: Reasonably successful tank cleaning

i know where u guys can prolly get the chemicals and dispose them 4 pretty cheap go to your local furnature refinifhing shop they can get u just about nething u want and most strippers are down to earth people who prolly wont charge u much i have also had sucess with naval jelly then mineral spirits then alchoholi got enough to do my tank and the leftovers dispose of from "'the strip shop" for 25$ and they let me use their tanks etc

Re: Reasonably successful tank cleaning

Tops of tanks get a deposit of tar like gum too because the fuel crawls up the tank as it evaporates. I start with the rocks in tank method but I find laquer thinner works best and I shake it upside down. Naval Jelly is phosphoric acid in gel form and you can thin it with water. I'll try the dryer method but will wrap the tank in rags. Access to a paint shaker would be ideal

Reasonably successful tank cleaning

I had saved this thread for future use and ended up doing it tonight. The tank looks awesome! I can't believe how well it turned out. That muriatic acid is some nasty stuff though. With all of the fumes and visible hazardous gases that it produced, my neighbors must have thought I was making meth or something. I don't think you can warn people enough about that stuff. Anyways, thanks Legendre!

Re: Reasonably successful tank cleaning

I used por-15 in my 1981 puch I got and it worked great! cleaned tank and sealed tank!

Re: Reasonably successful tank cleaning

Yes,it is some nasty stuff,but it sure gets the job done,and is not that dangerous IF you handle it properly,and take the proper safety precautions.I've been using it for 30 years and have no ill effects from it.BUT,I most definately would not recommend it that it be used by someone that has no experience with it.It was an experienced mechanic that taught me how to use it,30 years ago.Make no mistake about it,it can be very dangerous is not used properly.And don't get a macho attitude,like,ah,this stuff won't hurt ME.I assure you,it most certainly will.Jerry.

Re: Reasonably successful tank cleaning

New question regarding this technique: I Kreemed a tank 15 years ago or so, and I know about acid washes, but I found that the Magnum tank began rusting AGAIN within 24 hours if you didn's SEAL the tank immediately with the thick Kreem compound. None of you refer to sealing the tank to prevent rust from starting again, but some mention that their tanks started showing incipient rust. It would seem to me that merely doing an acid wash wouldn't solve the problem long term. Am I wrong?

Also, denatured alcohol is, if I recall correctly, anhydrous and is an EXCELLENT way for removing water from stuff. I learned about it refinishing furniture: A brush, water-wet from a final cleaning can be used almost immediately if dunked in denatured alcohol. And denatured alcohol evaporates in seconds.

Re: Reasonably successful tank cleaning

I did not seal my tank after the acid cleaning, I don't use sealer unless the tank is already leaking - period. I did use Coke (weak phosphoric acid) to condition the metal after I was done, and the tank has not res-rusted to date. Looks nice and clean in there.

Coke is nasty stuff, but I drank plenty of it as a kid. Wouldn't do that these days.. Wonder if Diet Coke has the same phosphoric content.. would remove any potential issues relating to sugar in the tank.

Next time I do this, I'll look into using the Behr's Concrete Cleaner product that MoPedLar mentioned. If it's a one-step solution, that makes life easier. Curious about the price, however.. phosphoric acid is much more expensive than muriatic.

Anyway... Do you hear that? It's sizzling... that means it's working! lol

Re: Reasonably successful tank cleaning

Thanks all so so much!!! My Columbia has spark!! A clean tank thanks to paint thinner, flush....Muriatic acid, flush....Coca cola classic, flush...denatured alcohol.....then the right gas/oil mix.

It started in 15 feet and purred like a kitten!!!. Now i just gotta get my lights to work

Re: Reasonably successful tank cleaning

Allen Murphy /

It's like this....

The muriatic acid eats off the old rust, and then the phosphoric will leave a layer of iron phosphate, like the Parkerizing on firearms.

After rincing, try using acetone--it's the same thing that we used to dry labware in chemistry labs for years, and you'll be amazed how much more water it'll pick up compaired to alcohol!

Seal with a sealer--POR-15. polyurethane paint, epoxy paint, and you're done!

Al Murphy

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