When I worked at a radiator shop we painted our finished jobs, BUT- - - -we held the spray gun at a 45 degree angle so only the outside 1/8" or so of the fins got painted. All the paint accomplishes is cosmetics- - - -for the ones we wanted to do the maximum cooling, like for race cars, we didn't paint those jobs.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!