Vinegar is an acid. How thick is the metal?
Hydrochloric is an acid also however it rarely matters how thick the metal is because thoroughly neutralizing that stuff including other acids is almost impossible on the hobbyist's levels.
I would like to add two or three things about this that no one (-especially on social media!!) ever gets right about offering these methods of Model-A gas tank 'fixes'.
(1) Any of these liquids (EvapoRust, Rust911, Vinegar, Molasses, et/al) will attack the rust however based on tanks we see, it rarely ever dissolves. Flushing rarely removes all of the iron oxide particles either. Therefore, you really need some way to remove the particles either by media abrasion or water pressure aimed directly at the base of the rust. Then when these particles are not removed, more often than not, the rust is still underneath where the particle was still attached.
(2) Most of these rust dissolvers also attack soft metals such as the Terne coating that was used on the metal prior to the tanks being stamped. So now after using chemicals, you have areas where the metal is unprotected. Without any coating, what is protecting the walls from rust reforming? So the answer most agree to is that it does need some level of protection. Some make an argument to keep the tank full at all times. That might seem plausible to some however most fuels have oxygenizers added which is the key ingredient that makes up iron oxide. So is really a tank full of gasoline the solution??
(3) So with the metal inside of the tank unprotected, what is the plan for recoating the tank walls? While you are pondering that question, to further complicate solutions, what is the plan when the tank is still located in the vehicle??
In a nutshell, any bare metal on the inside of a gas tank
WILL form rust again again, ...so we are likely back to the reason why most tanks are causing problems. The most universal way to address the bare metal problem is to line, -or coat the interior walls with a sealer that can protect the metal however not dissolve because of the fuel inside the tank. The key to successfully lining a tank wall where it will have longevity is to have good adhesion to
every area inside the tank. Therein lies the biggest reason we see failures. Now we go back to what we discussed in 'Bullet 1'. Unless you can clean
ALL the metal where it is absolutely 100% clean, the coating will not adhere properly (-look at the first 3 picture below of a tank that was cleaned chemically and then coated with a sealer).
The truth is, flushing just cannot get all of it 100% clean. Abrading all of the surfaces with media is the only way that all of the Terne and metal corrosion can be 100% removed. Additionally, the media blasting creates a texture that most urethane sealers can 'bite' into. This further enhances the sealer's adhesion which extends the longevity of the product.
Next problem we find is, most tanks never get fully coated. From what we have seen, using a quart of sealer in a tank that has been removed is not enough to coat everything including baffles. If the tank remains in the vehicle, the only way to ensure all of the baffles and the topside of the tank is fully coated is to completely fill the tank with sealer prior to draining. That means the tank will need to be completely filled with somewhere between 10 - 11 gallons of sealer!! Otherwise, please explain how all areas including the roof and backside of the baffles can have enough of a coating mil thickness to be effective. It is worth noting that if an area has rust formed around the perimeter of the Sealer, we have seen it over and over thru the years that the corrosion will travel under the Sealer causing more rust.
So in conclusion, adding Vinegar or any type of chemical rust convertor/dissolver to a tank is like suggesting that adding air to a flat tire with a nail thru it is the way you correct the flat tire. Temporarily it will seem repaired however it really isn't repaired and ultimately more damage is done to the tire.
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