I live in a place where the roads are salted and it leads to a lot of undercarriage corrosion. I typically get my vehicle undercoated every year (which costs about $150 where I am).

Even though I have undercoated it (typically via rust-check or krown) the frame still rusts (it's an old Jeep TJ).

My question is, is the undercoating doing anything beneficial if it's being sprayed on already rusted components? I'd rather not spend money if there's little to no value. And I wonder if it may actually be hurting things (by keeping moisture in).


  • What kind of undercoating?
    – gdelfino
    Apr 12, 2022 at 16:39

1 Answer 1


It will make it worse. The rust likely contains some moisture to promote corrosion. You answered your own question. Long ago, Amoco did testing on undercoating. When new and continuous it protected, but it aged and cracked. Then water, mud and road salt got under it and accelerated corrosion.

  • Thank you, I appreciate the response. Anything I can get out on the frame to slow down more corrosion?
    – hurlbz
    Nov 13, 2021 at 17:09

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .