I was looking at my flaking radiator which I just patched. I need to give it some paint. I'm going to get off the loose paint and I was thinking of just spraying the top and bottom and sides with black engine paint. Sound like a good plan? I don't plan on painting the core. I want as much heat to escape from there as possible.

Don't do that, The radiator needs to breathe. Eastwood sells radiator paint. I've used it and it works nice. I media blasted my radiator then painted it with radiator paint.
http://www.eastwood.com/ew-radiator-bla ... inish.html

I've painted radiators for decades with whatever black spray paint I have had lying around and it's worked wonderfully.
I'm with you on not painting core much, but I do give it a quick coat.
Keith

azyou- Don't paint what? The top and sides? I don't plan on painting the core itself, at all.