You can in fact buy black paint specifically formulated for painting radiators.
It apparently helps heat dissipation and copes with high temperatures.
Like Joe H mentions I imagine like any paint job,good prep is the key.

If I can remember who sells it i'll post a link.

Edit: Here you go. Radiator black.

Available in gloss or satin finish and it's on special offer just now! thumbs_up

Last edited by jockbolter50; 12/01/2014 9:44 AM.
1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.