Phosphoric acid tank rust removal, coating required afterwards?

[Chuck78]

I actually already bought 2 gallons of vinegar to use to derust my tank, but then I had read from several sources that the tank usually will flash rust immediately upon removal of the vinegar, which is not what I was looking for! I was hoping to not have to coat the inside of my tank, so using abrasives, bolts, chains, etc seems to me that it would just scratch up a tank more and leave more to rust.

I suppose my biggest question is, is there any coating on the inside of the tank from the factory that gets eaten away when using muriatic acid, other harsh products, or vinegar?
if so, what is the best chemical to use to strip or convert the rust that will not harm the tank's original coating?

secondly, does using phosphoric acid really leave a phosphate coating on the metal that prevents rust? is this a long term thing, or does it wash away after the first tank of gas? I have read some people saying that they chased the phosphoric acid immediately with acetone, because the popular Home Depot Behr Concrete Etch & Rust Stain Remover that is 45% phosphoric acid typically will leave a white chalky residue that will flake off if left to dry after draining and not rinsed immediately.

I barely had any speckles of rust in my good tank that now has a dent in the side of it after a deer collision, and this really nice replacement tank that I got from a fellow GSR member has quite a few speckles of rust, I would say one per square inch, but not very severe yet. I was hoping to remove this before it got worse or before any of the rust debris started causing carburetor problems, already have enough of those currently!

 

[tkent02]

Just a few specks I'd slap it on and ride. It won't rust if it's ridden and kept full.

 

[Chuck78]

More than just a few specs on the tank that will be going on my bike... Needing to give it some attention before installing.

 

[Guest]

In my book, if you're going to go through the effort of acid etching your tank to de-rust it, I would coat it with POR15 and be done with it... never worry about rust again.

When living in places where humidity is a factor, it's only a matter of time before the tank will rust again.

Of course if the tank exterior looks good now you just have to be extra carefull during the coating process & take precautions to keep it off the paint and such.

 

[Bill Alexander]

In my book, if you're going to go through the effort of acid etching your tank to de-rust it, I would coat it with POR15 and be done with it... never worry about rust again.

When living in places where humidity is a factor, it's only a matter of time before the tank will rust again.

Of course if the tank exterior looks good now you just have to be extra carefull during the coating process & take precautions to keep it off the paint and such.

What he said.

The POR15 has worked pretty well for me. It can be bought as a fuel tank repair kit and it is important to follow the instructions.

 

[jbthomp]

Make sure you use apple cider vinegar and not regular vinegar. The acid from the apples is what takes the rust off and it worked great for me. My original tank was badly damaged and I bought a good used tank but the inside was completely covered in rust. I soaked it in Apple cider vinegar for a couple days and it came out looking like new. There is some kind of coating inside that tank from the factory it won't flash rust that fast. I coated mine in wd40 and had it painted. 3 weeks later it still hasn't rusted. I don't believe in those gas tank coatings because if something doesn't go right it will make a huge mess out of your fuel system.

 

[Nessism]

The phosphate coated metal will be less prone to rust than other derusting methods, but it will still flash rust a little. I wouldn't worry about it though as Tom suggests. That Home Depot metal prep stuff is great stuff and the rust will be gone before you know it. It will turn the metal gray, which is the phosphate coating. I'd use the acetone after water rinsing and try to dry the metal as quickly as possible afterwards. Unless you have rust pitting in the metal, I'd let the tank alone after cleaning and derusting. If the tank has deep rust pitting, that's when you should consider going with the Por-15 kit. BTW, the kit comes with phosphate sauce so that should tell you something about the best material to derust with.

 

[chuck hahn]

I am with Ed. the tiny little brown coating that appears isnt squat in the big picture in my experience. Clean it, rinse it out, and use somethnjg to dry it rather quickly and fill with gas.....done.