not entirely sure but you can buy heat resistant radiator paint in spray cans and that seems to work ok. i sprayed a rad including the fins on a mk2 escort in matt black and it looked ok. i don't remember any paint flaking or going discoloured nor did it affect the temp. i did not spray several coats as i thought that might block the fins. i wouldn't think there would be a lot of difference between an intercooler and rad. i would say however the rad was in very good condition before spraying.