epoxy primer is very strong & will outlast most cheap paints but i would have it top coated with a good quality automotive paint as well, not a cheap spray can paint.
if the rust was only on the outer surface it should last a long time, but if its coming from the inside out, no paint/primer will stop it, just covers its up cosmetically.
Quoted for truth! I went through this a few years back when I bought my 4Runner. The truck was in great shape mechanically and cosmetically, but the frame was very rusty. I figured, “no big deal, I’ve been sandblasting and restoring cars my whole life”. Let me tell you, these Toyotas have an intrinsic design flaw in the frames, and quite possibly even in the metal used to construct them so they do rust from the INSIDE out! I did a “white blast” on my frame, meaning completely clean of all rust and other coatings, and a few years later, not only has it started coming through in several places, now I actually have holes in the underside of the frame in several places THAT CAME FROM UNDER THE PRIMER/PAINT! This, I believe is similar to why a lot of Jeep CJ frames rotted out. It is a a boxed frame design, with plenty of holes in the sides, but no where for water, sand, and salt to get out! No matter how well you blast and paint the outside, the only chance you’ll have of staving off the corrosion is to somehow coat the inside with oil, Fluid Film, Eastwood internal frame coating, etc. Problem is that you have very little actual access to KNOW that you coated it completely. If using oil and you just blast tons of it in there, you may flood the bottom, which will help for awhile, but then you’ll be dripping it all over your driveway and everywhere you go for months, which isn’t super practical or environmentally friendly. If you’re like me, and have a brand new driveway done in the last two years, the last thing you want is a bunch of oil patches all over it! That is why I didn’t oil the inside after painting it last time, plus it makes any future repairs trying to weld patches in a nightmare down the road. My personal plan at this point is to cut out the bad areas, then while the frame is open, blast, prime, and paint as much as I can get to. Then I will weld in the replacement sections, also coated on the inside, then blast the outside and coat the repaired sections. Is it a perfect plan, no, but I believe it will buy me several more years of vehicle use and life, and is the best chance to make sure at least the repaired sections will stay solid for many years to come.
