I was doing an oil change on the wife's Protege5 yesterday and noticed that most of the frame rails (its a unibody of course), have rust on them. At one point they were painted/coated black at the factory, and the car has been either Krown'd or Metropolitan rustproofed about 5 times in the past 8 years. Now, however, about 50% of the surface area of the frame rails shows rust, although I did not see any true holes in the frame.
Is there a way to stop this or at least slow it down? I have a suspicion that Krown or any other spray-on oil film like it, will not stay on the underside of the car through the winter salt barrage with road spray, etc. I was thinking of the Rust-Check "Coat & Protect" spray which is like a spray-on gel that doesn't drop, but it also doesn't really creep as much as a fluid film product either.
Should I take the wire brush wheel and my drill to the frame rail to clean it up and then use a particular product to seal it? Or is there a better way? Or, just leave it be and forget about it (We plan to keep the car for another 5+ years, most likely).
