hate to argue strutto, but painted aluminium is far worse at heat exchange than the raw alloy.... just think to early 80's F1 cars and CART cars... no paint there! GTR man 1992 got it in one.... it is insulation, and is not good at all, the only reason cars had it was asthetics... i.e. to blend in... same deal for competion radiators etc...
so if you can strip it safely ( i.e. not harming the metal, do it....)