[rattus]

My mistake (iron not steel). But iron will still reflect much more IR than black paint. Iron is actually pretty shiny, its the oxidation that makes it look dark (if you buff off the oxidation it'll look fairly shiny). Dark oxidation will act like like black paint if it has similar absorption properties.

Also the black paint doesn't reflect the energy back to the engine it absorbes it, then emits it. There is a difference... if the IR energy is mostly reflected (as is the case w/ light, shiny or metalic paints) there is little energy transfer into the paint's atomic/molecular structure, the energy goes right back to the iron and thus less of the energy is transfered to the air. When the black paint absorbs the IR energy, its absorbed into the paint's atomic structure (electrons are bounced up into higher energy states) and then emitted equally in all directions, i.e. air and iron.