Be sure to use a paint that's specifically designed for radiators, and don't coat the fins heavily. Some paints serve as insulators and will interfere with heat transfer. Also, spray at about a 45 degree angle so only the first fraction of an inch of the fins actually gets painted.
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!