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post #1 of 15 (permalink) Old Jul 20th, 00, 02:49 AM Thread Starter
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Bruce
 
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now that i got my cam problem figured out, here's a question on what color to paint the engine. i always paint my engines black, and a fellow co-worker asked me why ? i was always told by my engine builder, and a man i knew,whom owned a machine shop that built iroc engines, that black helps to keep the heat away. well several years later, i still can't figure out why black helps to keep the heat away. weren't we always told that black absorbs, and light colors reflect heat ?
can anyone give me a reason for this ?
thanks,
bruce
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post #2 of 15 (permalink) Old Jul 20th, 00, 04:12 AM
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black absorbs LIGHT (which converts to heat)and white reflects LIGHT (which is why white cars feel cooler than black cars).

Now, why black is a better color for heat dissipation is a good question. I had heard that before too, but I can't believe it would have a dramatic effect on underhood temperature.

I like chevy orange

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post #3 of 15 (permalink) Old Jul 20th, 00, 05:37 AM
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i've never heard of the black keeping the engine cooler(but im still young), but what about canary yellow? well i guess it depends on what color car u have. a friend of mine has a yellow 75 stingray w/ a canary paint job w/ lots of chrome goodies on it....it looks good. i keep tellin him he should put a mirror under the hood to catch all the brightness (its a show car, not street). neways i guess the color of ur engine depends on the car color.

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post #4 of 15 (permalink) Old Jul 20th, 00, 06:02 AM
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The color black is supposed to dissipate heat faster, why I do not know, I'm not a scientist. I would be willing to bet that if you had a engine painted black and then painted it something like orange there would be no noticable difference in operating temperature, with so many variables in a cooling system I can't see the color of an engine having a dramatic effect. I've read that an allumimum radiator company suchas BeCool or Griffen, I can't remember which, is offering black painting on there radiators which they claim will reduce temps by X% amount, black dissipating heat faster being the reason.

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post #5 of 15 (permalink) Old Jul 20th, 00, 06:20 AM
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Black doesn't reflect heat, it retains it. If you put a black and a white cast iron skillet out in the sun, the black skillet will get hot because black absorbs the heat. The white skillet will stay cool because white reflects heat. I actually remember this from a film I saw in science class in grade school.

Applying this to an engine, heat that exists thru the cooling or exhuast system is wasted. The more heat you can retain in the engine the better (I'm sure only up to a certain point). I would suspect that racers paint their engines black because they think the engine will retain more heat.

From a more practical standpoint, I painted my engine black because it is harder to tell when it is dirty. Those pesky little leaks just don't show up on black like they do on other colors. I also have no underhood chrome as I would rather spend my time driving my car than cleaning the engine compartment.
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post #6 of 15 (permalink) Old Jul 20th, 00, 06:29 AM
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Black is the absense of color.

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post #7 of 15 (permalink) Old Jul 20th, 00, 06:30 AM
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I think ken has it right, black absorbs the most light rays which turns into heat. If light is not a factor, then black will dissipate heat fastest.
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post #8 of 15 (permalink) Old Jul 20th, 00, 07:50 AM
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Paint it any color you want.I dont believe anyone has had cooling system problems because of the color of the engine.At least I never heard of it in my very short career at a radiator shop.
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post #9 of 15 (permalink) Old Jul 20th, 00, 07:51 AM
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Paint it any color you want.I dont believe anyone has had cooling system problems because of the color of the engine.At least I never heard of it in my very short career at a radiator shop.
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post #10 of 15 (permalink) Old Jul 20th, 00, 01:51 PM
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This is the scoop. Black will absorb and dissapate heat faster. The reason is black has a higher emissitivity or "k factor" for you senior theromdynamic students. That's why you want to paint your radiator black and not leave it copper. (Flat or satin black would pass more heat than gloss black) There is actually a formula in my old text books somewhere where you can figure the k factor by using a color scale relative to ambient light. Forgive me if I don't try and find the book.
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post #11 of 15 (permalink) Old Jul 20th, 00, 02:59 PM
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Chevy orange works for me.....kinda maintain that "stock" look....as in "stealth"..."looks stock, can't be that quick"....
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post #12 of 15 (permalink) Old Jul 21st, 00, 03:58 AM
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According to a section in "How to Hot Rod Small Block Chevys" Pg.146

"ALCOA's (as in aluminum)compares an as-cast surface with one which has been black-anodized to a depth of 1.7 thousandths. The black surface is MORE THAN TEN TIMES BETTER IN HEAT-RADIATING ABILITY THAN A PLAIN CAST SURFACE."

The main argument leading to that statement was against polished/shiny engine parts. But the point is...in aviation, racing and industry when you're trying to dissipate heat, or promote it's transfer elsewhere... Black does the trick. What color is YOUR radiator...even if it's factory aluminum?
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post #13 of 15 (permalink) Old Jul 21st, 00, 05:57 AM Thread Starter
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well i talked to one of the engineers i work with and he went into a big scientific reason why black will run cooler. we are correct in thinking black will get hotter when you are heating it from the outside. ie, black shirt in the sun.
but as he told me, you are heating it from the inside, so the heat leaves the block and reflects it away. he told me that this is subject that is one of those things that can't be explained. but he did assure me that a black engine will run cooler. he also said flat black is better. and i take his word, he is a very smart person. he has all those frame pieces of paper hanging on his office walls.
thanks,
bruce
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post #14 of 15 (permalink) Old Jul 21st, 00, 07:42 PM
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Framed pieces of paper on his wall? I do too,old speeding tickets!

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post #15 of 15 (permalink) Old Jul 24th, 00, 04:22 PM
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Well guy's finally something I know. I am a Mechanical Engineer with a speciallty in heat transfer and thermodynamics. You are right, I won't go into the science of it, but the blacker a body is the better it will radiate heat. Also the better it will absorb heat, so it all depends on the temperature difference between the surface of the engine and the outside air. Assuming the same temperature difference a black body will transfer more heat than a lighter color. However, I really don't think painting your engine black will do much for the performance if your cooling system is functioning correctly. The key is to have the engine operating at the correct temerature and as long as your radiator is transfering the heat there is really no reason to use the block to transfer any more heat to the outside air.
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