My 59 Tbird has undercoating everywhere there wasn’t paint. I attempted to remove some to see what I would be in for. It’s a mess, tarry rubbery, gets everywhere and sticks to everything. Should I even remove it? Anywhere it has been applied it has worked well, no rust. Or does anyone have a good solution to removing it? I like the clean look and if I had/afford a rotisserie it would be a lot easier. Any suggestions would be appreciated.

Generally, heat and a razor blade scraper will remove it. However, if it is still doing its job you might consider leaving it. I have done that on a couple of cars after removing some of the undercoat for welding purposes. Once done I simply added some fresh undercoating where needed.

YEP, i wouldn't remove only what you need to for welding, its good stuff. look what it did for 60 years. and its much better that the new stuff you'll get in an aerosol can.
Jay D.

That’s exactly what I was thinking, is there anything I can spray on to freshen up the appearance without creating a moisture pocket? Thanks!!!

i'm not sure what you could use to clean it real good. that old stuff is a petroleum based product so any solvent type products or gas and diesel are going to eat it up. you might try a heavy cleaner like Simple Green or a Citrus cleaner of some type. I would spray the S/G on and let it set for a few minutes then hose off. I would defiantly try a small spot first to see what its going to do.
Jay D.

prolly same type of UC i found on this. i had to replace steel on the lower doors and getting that stuff off to weld in new steel was a mess and time consuming.

Sorry I didn't follow up sooner, was at work and it ended up to be a fairly crazy busy weekend. Yes it definitely is petroleum based, I was thinking it might even be hazardous LOL, what I meant is it looks "old" but is thick and gooey totally filled one of my wire wheel brushes on a 4"x4" area. What I meant is besides areas of repair, what I would leave on the car, which I would say is better than 80% what could I use to spray over the top of the old to make it look fresh without causing harm, so by appearance it looks good? In the same manner anything exposed would get coated whether by undercoated and the top coat for conformity or if you think a top coat of undercoating over everything would be okay?

I use a product called DEI BoomMat (spray can) for undercoating
wheel wells, inside doors, etc. It should work for touching up your
old undercoating, if that's what you want.