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Why do black cars so much hotter than white cars on a hot day{parked } ?? Sittng on a black seat vs white certainly seems to be a difference. I always thought black absorbs and white reflects ?? Dunno



Both are true.

Heat is transmitted by 3 different methods. Conduction: traveling within the material of an object (why the wire you're soldering is getting hot further up the wire from the solder location)
Convection: moving via air (or water) transfer to another object (hence, convection oven). Radiation: radiating the energy to the surrounding atmosphere or space. (Used commonly on spacecraft for supercooling components.)

Dark surfaces radiate better than light surfaces. But dark colors absorb light well also. They get hotter simply because they absorb light energy faster than they can radiate it. So even though light colored cars do absorb energy and radiate it to some degree, the main mechanism is reflecting the energy in the first place instead of absorbing it.

A black radiator will radiate better, but the main mechanisms for heat transfer in a vehicle radiator are conduction (transferring through the walls of the fins/tank of the rad) and convection (transferring it to the fluid [air, is this case] traveling through/around the radiator.)

HTH,
Marq