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Author Topic: Forget the myth about black paint and hot cars
snopes
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For 20 years, I have urged people in this shadeless, concrete-slathered sector of Texas to avoid black cars because they are generally hotter than the surface of the sun.

As it turns out, I was only partly right – a surprising discovery I made recently during a little experiment conducted by Craig Eppling, the regional head of public relations for General Motors Corp.

http://www.dallasnews.com/sharedcontent/dws/bus/stories/0901dnbusBCColor.2d3b24f.html

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Dear Babby
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Not a well-controlled experiment. They were testing the effects of tinted widows and windows left up or down as well as of car color.
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Lonely Mountain
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I always thought that dark cars just heated up faster than lighter cars but if left out long enough, they both will heat up to the same temperature. Am I just completely wrong? [Confused]

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DonSample
I'm Dreaming of a White Sale


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Three different models of car, too. Mythbusters did two identical cars, one white, the other black, and the black car got about 10 degrees hotter.

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DaGuyWitBluGlasses
I'll Be Home for After Christmas Sales


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there's a lot of insulating space between the paint and the interior, so the paint shouldn't effect the inside.

However black coloured cars can get a(n outside) surface temperature around 100 C.

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Errata
Happy Xmas (Warranty Is Over)


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quote:
Originally posted by Lonely Mountain:
I always thought that dark cars just heated up faster than lighter cars but if left out long enough, they both will heat up to the same temperature. Am I just completely wrong? [Confused]

Not necessarily. The inside of a car can actually get hotter than the air outside. Intense sunlight imparts energy, but the air cools it off. It would make sense then that a car that heats up faster will also have a higher maximum temperature when the heating of the sunlight and the cooling of the air reach an equilibrium.
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Delta-V
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quote:
Originally posted by Errata:
quote:
Originally posted by Lonely Mountain:
I always thought that dark cars just heated up faster than lighter cars but if left out long enough, they both will heat up to the same temperature. Am I just completely wrong? [Confused]

Not necessarily. The inside of a car can actually get hotter than the air outside. Intense sunlight imparts energy, but the air cools it off. It would make sense then that a car that heats up faster will also have a higher maximum temperature when the heating of the sunlight and the cooling of the air reach an equilibrium.
IIRC, one of the problems is that normal automotive glass is transparent to visible and near-infrared light (but opaque to UV), which heats up the interior. But the glass is opaque to far-infrared, which is what is re-radiated from the hot interior, and therefore traps the heat in the car. There are some newer glass treatments that cause it to be reflective to near-infrared, which helps considerably.

The car body acts as an insulator. Since the interior cannot re-radiate the heat back out, it has to conduct it through the body and windows to the outer skin of the car. The outer skin is then cooled as air passes over the car as well as radiating it off. The amount of cooling is heavily dependent on the temperature delta between the air and the car's surface. The car heats up until the incoming energy equals the outgoing energy.

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"My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere

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