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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

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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

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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

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if painting a bare core made it transfer heat better...then why do all new autos come with a bare aluminum radiator core?

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To save money I would imagine...since the tanks are plastic, and the core is aluminum, there is nothing that will oxidize and look bad to consumers, so why not leave it ?

And a buddy of mine here worked at Alpine for quite a long time, he was in amplifier design for a while and they did a bunch of tests to see which was the best coating to help shed head from them...a matte black finish tested (and as said, should have basically) to be the best thing to help them shed heat.

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I was always taught and told that a black radiator would shed heat more efficiently. The only reason I can think of on the newer ones is because they design them with better capacity/tolerances, ie., more tubes, etc. or they don't need the transfer because of lower horsepower? Copper/brass is actually far more efficient than aluminum at dissapating heat. Aluminum is only good because they can put more tubes in the core. But you are WAY better off if you can use a copper brass bigger radiator than aluminum. Just the laws of physics.

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Kinda off topic here, but aluminum rads are better than brass / copper at removing heat - not because aluminum is a better conductor, but because you can make the tubes bigger with aluminum than brass ( it's stronger ) so you don't need as many rows of tubes for the same flow. Heat transfer efficiency drops way off with the 3rd & 4th rows of tubes ( over 50% )on big brass radiators. Aluminum rads usually only have 2 rows of tubes, but the tubes are big - 1/2". Same flow as 3 -4 row brass rads, but better heat transfer on the 2nd row verses the 3rd and 4th rows of brass rads. Did I mention lighter

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I was always taught and told that a black radiator would shed heat more efficiently. The only reason I can think of on the newer ones is because they design them with better capacity/tolerances, ie., more tubes, etc. or they don't need the transfer because of lower horsepower? Copper/brass is actually far more efficient than aluminum at dissapating heat. Aluminum is only good because they can put more tubes in the core. But you are WAY better off if you can use a copper brass bigger radiator than aluminum. Just the laws of physics.

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Kinda off topic here, but aluminum rads are better than brass / copper at removing heat - not because aluminum is a better conductor, but because you can make the tubes bigger with aluminum than brass ( it's stronger ) so you don't need as many rows of tubes for the same flow. Heat transfer efficiency drops way off with the 3rd & 4th rows of tubes ( over 50% )on big brass radiators. Aluminum rads usually only have 2 rows of tubes, but the tubes are big - 1/2". Same flow as 3 -4 row brass rads, but better heat transfer on the 2nd row verses the 3rd and 4th rows of brass rads. Did I mention lighter

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the stock aluminum radiator that was in my Dakota is only a 1 core radiator! but the core is 1" thick, the tubes are long and oval shaped, and it keeps my stroked, aluminum headed big block cool even when driving through traffic in 90+ heat

and the lack of paint might be a cost thing. I don't really know.

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if painting a bare core made it transfer heat better...then why do all new autos come with a bare aluminum radiator core?

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All new cars are designed to run Hotter , maybe an emissions thing , so why bother to paint the Radiator to make it run cooler , that is my guess.

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I believe radiators were painted black because they felt a black radiator was cosmetically more appealing than seeing a bright orange core through the grill

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Also consider that if black was so much better at cooling, NASCAR cars would have black radiators where even 5* would be a great benefit.

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"Home > Library > Miscellaneous > Britannica Concise Encyclopedia

Thermal Radiation

Process by which energy is emitted by a warm surface. The energy is electromagnetic radiation and so travels at the speed of light and does not require a medium to carry it. Thermal radiation ranges in frequency from infrared rays through visible light to ultraviolet rays. The intensity and frequency distribution of the emitted rays are determined by the nature and temperature of the emitting surface; in general, the hotter the object, the shorter the wavelength. A hotter object is a better emitter than a cooler one, and a blackened surface is a better emitter than a silvered one. An example of thermal radiation is the heating of the Earth by the Sun.
For more information on thermal radiation, visit Britannica.com. "

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Honest question then...not being sarcastic

From what I read here, a black metal roof will actually be better in the summer for cooling my house vs a white metal roof? Is this right? (based on the argument presented for radiating heat?)

eightlitermopar

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Uh, no. "A hotter object is a better emitter than a cooler one" I would assume that the temperature of your roof is cooler than the temperature of the sun.

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From what I read here, a black metal roof will actually be better in the summer for cooling my house vs a white metal roof? Is this right? (based on the argument presented for radiating heat?)

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Come on guyz ...common sense ...

ANY paint on a rad is going to PREVENT(and insulate) the best heat transfer from the rad to the outside air.

The reasons WHY they are painted(oEM) is to prevent or retard outside corrosion.

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I know it goes against common sense. BUT- Just how does a positraction rearend work in a 67 Plymouth?? It just does!!