StingrayL82 -
Assuming you want to paint the gas tank and prevent further exterior corrosion:
Use a
rust converter instead of a rust remover. (
Alternate description.)
One of my businesses, Riffgan Restorations, includes what you're doing. Specifically, restoring older motor vehicle parts. On thicker metal, I use rust remover. On thinner metal, I use rust converter. (I prefer completely removing rust but with thinner metals there's a risk of penetrating the metal.)
Rust remover consists primarily of phosphoric acid, with surfactants to aid penetration. (3M Scotch Brite pads are the secret behind using rust removers.). The phosphoric acid leaves an iron phosphate coating that partially inhibits corrosion and serves as a primer. (Check the ingredients labels on Coke and Pepsi cans.)
Rust converter consists of tannic acid and polymers. (Some rust converters include phosphoric acid as a minor ingredient.). The tannic acid converts active rust into an inactive form and the polymers seals everything. Rust converters also serve as a paint primer.
Both of these require removal of all loose rust and dirt prior to application. You also need to thoroughly remove any oil and grease. Otherwise, you wind up wasting rust remover or rust converter and are often left with incomplete removal or conversion.
I use a multistep process for cleaning. Tuff Stuff Cleaner and a stiff brush for heavy concentrations of oil and grease. Dish soap, TSP, and hot water, with a stiff brush, rag, or Scotch Brite pad, followed by a hot water rinse. Denatured alcohol rinse to remove remaining rinse water.
Depending on how the part is going to be finished, I usually follow those steps with a commercial cleaner/degreaser/wax remover, acetone, MEK, or other solvent. I usually follow with a phosphoric acid etch or a phosphate coating.
Load bearing parts, such as caster shims, get a manganese phosphate coating and a corrosion inhibitor. (Assuming I have a heated tank large enough to hold the part.)
Phosphate coatings create issues for some powder coating so I often stop at 'bare' metal and start the powder coating with a zinc-rich primer powder.
The result is an equal to or better than new part.
(No, I haven't included some of the special things I do, such as using Hi-Temp Lab metal to fill pits.)
