De-rusting the gas tank a better way than vinegar...

[Bminder]

I tried de-rusting my gas tank with vinegar a couple weeks ago, and I read about how quickly it will flash-rust after that. But I thought 'quickly' meant a couple hours... nope. We're talking nanoseconds.  I didn't get some Heet or oil into the tank fast enough and it flash rusted.  So I put some more vinegar in it over night, and it didn't get it that clean the second time probably because I didn't wait 4 days again.

So after googling and reading dozens of posts on all kinds of motorcycles boards about derusting gas tanks, and all kinds of opinions on what to use, I decided to try phosphoric acid.   
Muriatic acid seemed too much hassle with how strong it is and the hassle of getting rid of it.  Vinegar takes days, and I wanted something faster.  The fancy rust-away products cost $25 a gallon, and I didn't want to spend $125 on 5 gallons to derust the tank.
Phosphoric acid also doesn't seem to harm paint or aluminum from what I read.  It's one of the ingredients in Coke and Pepsi, so it's not crazy toxic.

This moped website really helped explain the options: http://www.mopedarmy.com/wiki/Removing_rust_from_a_gas_tank
It recommended Behr Concrete Etcher and Rust Remover, but Menards had this product called Krud Kutter Concrete Clean and Etch, a gallon was $12.99, so I got 2 gallons because it recommended diluting with water.  Whatever product you buy, make sure it has phosphoric acid in it, and not sulphuric acid or something else like that.

I also got one of those big plastic under-the-bed tubs from Walmart to catch fluids.
2 bottles of Heet, or any similar product to help remove the water.
A small box of baking soda.
5 gallon pail.
A chair to sit on.
A new fuel filter.
A garden hose connected to a water supply.


So here's what I did:
1. Put rubber gloves on and drained and removed the tank. (I use those cheapy blue gloves you get 100 in a box for a few bucks.)
2. Closed the petcock, put a little fresh gas in and swished it around, rotated the tank around as I swished it, took off the petcock and drained it into my plastic tub.
3. I repeated that 2 or 3 more times till the gas came out clean as it seemed it was going to get. You have to put the petcock back on each time, but you'll get good at it   You can see how much crud is coming out each time you drain it into the tub.(After each rinse I poured the dirty gas into an old gas can.)
4. Put the petcock back on and put some water in, swished it around as I rotated the tank, drained it into the tub to see if anymore crud came out. I did that 2 or 3 times.
4. Shook all the water out I could, put the petcock back on.
5. Poured the 2 gallons of concrete etcher in and topped it up with water. It foamed so I had to go slow. I left the gas cap open, and laid a shop towel over the filler opening so no junk fell in.
6. I let it set for 4 hours. (I wasn't sure how long to let it set, but this tank only had flash rust and wasn't that bad, and after 4 hours the inside was super clean.   I was impressed. The metal in the tank looked great, and I read that phosphoric acid neutralizes the rust and creates a coating on the metal that doesn't let it flash rust as easily.)
7. Before you drain the solution, get a 5 gallon bucket of warm water ready, and mix in half a box of baking soda. This baking soda water is going to neutralize the phosphoric acid left in the tank.
8. Take your tub and the bucket of baking soda water to the curb and get your garden hose running at the curb so it will dilute and wash the solution away and you can rinse the tank again. And a chair to sit on.
9. Drain the solution into the tub, you can see if any more rust comes out. It's kinda tricky to tilt the tank to remove the petcock, solution came out the gas filler, phosphoric acid didn't seem to hurt the paint, but I was quick to rinse it off anyways.
10. Put the petcock back on and pour 1/3 or so of the baking soda water in, swish it around as you roll the tank over, take the petcock off and drain.
11. Repeat 2 more times with your baking soda water.
12. Take your garden hose and rinse out the tank with the petcock off.
13. Shake as much water out as you can get. It's hard because the tank is shaped so funny. You'll get the hang of shaking it just right to get almost all of the water out. Some guys take blow dryers or air compressors and blow it dry, but I didn't. I got as much out as I could, and figured the Heet and the Marvel Mystery oil I used next would get it all out.
14. Put the closed petcock back on and pour a couple bottles of Heet in. (or any similar kind of alcohol product.) Swish it around as you rotate the tank a couple three times.
15. Drain it into your tub, it should be really clean. Shake as much out as you can get.
16. Put the closed petcock back on and pour in a bottle of Marvel Mystery Oil, or whatever oil product you want to do. Swish it around as you rotate the tank a couple three times.
17. Drain it into your tub. Drain out as much as you can, but you don't have to get it all out because it's ok to run through the motor.
18. Clean the petcock out real good with carb cleaner or something similar.
19. Put the petcock back on, with a new fuel filter. Make sure the petcock is open
20. Put the tank back on and you can handle the rest from here.

Anyhow, that's what I did. I wish I had done that instead of the vinegar.

[rktmanfj]

Phosphoric acid, you say?   

Where'd you get an idea like that?     

[Pezman4200]

I'm going to revive an old thread to offer thanks for Bminder for writing his post!

This worked flawlessly!  I am reviving a 91 JF that has spent the last 12 years in a garage with no storage prep and the tank was in horrible condition. Rust central!  Wasn't sure what to do to get rid of it but stumbled upon this post and all i can say is WOW!!  Tank is looking great inside!  Not going to say its perfect but pretty close.  Couple tarnished areas but definitely as close to perfect as it could get.  Better than I could have expected.

One thing i did during the rinsing part was to rinse over a towel and every time I emptied out the tank id flip the towel (or get a new one) to see how much more rust came out.  When it was down to nothing but clear water........done! I should have taken a pic of the first few towels (and this was after i washed all the heavy stuff out before i started)

So, Bminder, THANK YOU, THANK YOU, THANK YOU!!