i was just looking through the picture gallery and i saw a detailed engine, and i noticed the radiator was painted black, is this bad, or is it ok to do it?
It's okay. Protects from external rust. I don't think a coat of paint will affect the cooling effects too much.
If you paint it, you should used a water based paint, some paint will actually act as an insulator and restrict the heat transfer, or thats what they told me at the rad shop that re-build mine.
i agree. enamel based paints will prevent heat transfer. you always need to use a water based for radiators