Using the wrong paint on a radiator can cause severe overheating problems. It's a heat exchanger, and painting it interferes with that process. If you decide to paint the core, use flat or semi-gloss black, and spray the fins at about a 45 degree angle so only the first fraction of an inch of the fins get painted. Don't let the paint penetrate very far into the core.
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!