Guys;
I'd like to chime in on where this discussion has drifted...yes, it's called a Radiator, and this (correctly) suggests one mode of shedding heat, and it also (but incorrectly) suggests that this is the predominant heat shedding mechanism.
Heat-shedding by the Radiator of a car occurs by two mechanisms: Conduction and Radiation. Conduction...is (by indirect Contact) to the cooler air which is pushed, pulled or otherwise directed through the high surface area...if this forcing were to stop (when Engine/Fan stop, and when we park the car, or even when we go very slow in a traffic jam), Conduction continues, but drops back to air Convection (this refers to density driven flow only...it doesn't even refer to transfer of thermal energy, although that is what is causing it). Air Convection alone (when car/engine are moving dead slow or even stopped), air flow is simply not enough to give the cooling our cars need, that's why the engine also drives a fan to help with this, and hence a lot of threads in the summer (when Conduction is also to much warmer air) from owners experiencing overheating concerns.
Radiation is certainly also occurring, but it accounts for only a small percentage of the heat shedding that is going on...to support that assertion, I would say that a car radiator even has the shape of a poor thermal radiator (it has just not been optimized for this), because most of its surface area is pointed to other parts of itself, not away, as it would need to be if radiation was the prime shedding mechanism...a car Radiator is optimized for Conduction process with high surface area to airflow...unlike the space shuttle...it must also shed lots of waste heat...but since it cannot do this by conduction to outside air, it MUST shed by radiation only...and the shuttle doors with their huge (and open) surface areas are used (and optimized!) for this...if the shuttle doors cannot swing open for some reason to radiate away waste heat, that Mission is done and they need to come home! This has almost happened at least once! Further, color of radiating surface does affect the efficacy, but not enough on a car Radiator to make any kind of significant difference (again because radiation is not its prime mechanism). Paint on a car radiator is mostly to protect metal surface, not to increase its effectiveness! Heatsinks on electronic equipment are often Black anodized, but also clear (natural alu color), because here on earth, the heat sink on a piece of electronics again works predominantly by Conduction.
In the engineering world, it would more appropriately be called a Heat-Exchanger to prevent a biased understanding of the shedding mechanism...hope that sheds some light...or Heat!
Cheers
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