Caswell is about the only treatment that I haven't read a bad review on .
I used oxalic acid . Here's an excerpt from my build thread :
This was an experiment for me . My Simplex had a bit of rust forming in the gas tank . Not too bad considering the bike is 55 years old . I'd read that different acids worked for removing rust .
I used muriatic acid to clean my XT350 tank with decent results . That tank did flash rust and I retreated it and then neutralized the acid ASAP . It still formed a small amount of flash rust . I'm running it with an in line paper fuel filter and haven't had any problems .
The Simplex tank is a bit more rare and harder to find . I was reluctant to use muriatic acid in it for those reasons . Through research , I read about oxalic acid , sold as wood bleach . Oxalic acid is a lot safer to work with , but still requires due caution ( READ THE LABEL ) . It's not nearly as toxic as muriatic acid . It does NOT harm painted surfaces . It just eats rust and leaves a protective coating on the steel after being thoroughly rinsed with water .
I used a diluted mixture from what is suggested , which is 12 ounces to 1 gallon of water . I used 12 ounces to 2 gallons of water . Being as the solution was weaker , I left the mixture in the tank twice as long and the results are shown below .
One last thing : Use a heat gun or hair drier to thoroughly remove any remaining water after the last rinse and empty .
This is what I used :
Here's the rusted tank :
And, here's the tank after being filled with oxalic acid for a couple of days :
This stuff really does work great . I'll use it from now on when treating rust .
Here are a few other things I've treated :
Before :
After :
You can see where I wiped some of the protective coating off the black plate in the last pic .
