most paints these days are "systems", especially specialized paints like tank sealer. The phosphate coating left behind by phosphoric acid that they tell you to use with POR 15 tank sealer is recommended for a reason. Regular POR 15 sticks best to a light rust haze, much better than to bare metal, the reason is the chemical bond of light rust to base metal. Flaky rust is as different thing. With this said, POR 15 tank sealer sticks best to the phosphate coating left behind by Phosphoric acid, not hydrochloric or sulfuric. Acid etch used for car bodies in body shops is phosphoric acid. There may also be other paint systems that use other acids. Follow the manufacturers recommendations to the letter and you will get good results. If tank sealer fails, it is because it did not stick to substrate (coating on the base metal). THe acid cannot produce this layer on top of the metal if it cannot penetrate the varnish and other stuff on the surface. Acetone may be great to dissovle varnish, but it will not convert rust, OR convert a clean metal surface to a phosphorus substrate that the POR 15 system is designed to stick to. Buy a new tank for 200$, it is the best option, for one you can't find a new made example, seal it because you have no other option. Sealing a tank will cost you 60 bucks or so. I have a 64 gmc with a sealed tank of 2 years and still going strong. The inside was shiny but it had rust holes from the exterior tank straps. When I cleaned it with the POR system, all kinds of brown crap came out every flush, and that was with what looked to be a clean tank to start with.
Hope this helps
Last edited by Fireballv8; 04/09/2008 4:13 PM.
