I would like to repaint just the fin half of this radiator that is rusted. I would like to know of there is a special treatment due to rust that I should do. I do plan to sand the rust with a grinder and a flapdisk.

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  • Well make sure you get your leaky bleed valve fixed first (if it isn't already) so the stains don't come back
    – cutrightjm
    Nov 30 '15 at 7:26

that looks like just surface rust. wipe it with strong citric acid or some commercial rust remover (like CLR or Limeaway). if it all comes off, its just some rust that has dripped down from the upper port. assuming there are no current leaks, you can just wirebrush it off and seal with a rust converter (corroseal or 3m marhyde are by far the best at this job) and then repaint the whole thing with a good quality latex or polyurethane (it will flex when heated).

just be gentle. remember, a radiator is a pressure vessel full of hot water.

  • But if I can remove it mechanically, there should be no need for chemical treatment, no ?
    – amphibient
    Nov 29 '15 at 20:57
  • 2
    rust is ferric oxide. its a crystal that grows. there is virtually no way to remove it from the micropores in the surface of the steel or iron. therefore, you remove what you can see, and then treat chemically to inhibit the crystals growth. otherwise, the rust continues to grow under the paint. paint slows it down, but won't stop it. passivation or conversion stops the rust, then the paint ensures it won't start again in a new place. Nov 29 '15 at 21:17

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