How to remove two-component adhesive from a stainless steel surface?
1) Heat gun - use a blow dryer or heat gun to soften the solution up.
2) Acetone - apply acetone to the spot. This will not penetrate the metal on the radiator.
3) Scrape - You can use an old t-shirt, stick the metal scraper inside the t-shirt and start chipping/smoothing away at the spot.

Repeat until it gets almost level with the radiator. You probably won't get it all up after the first pass.

After you do it again, you could get some medium grit sandpaper and try to smooth it away. Spot may still be there but raised surface shouldnt be nearly as bad.