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Old 04-14-2009, 03:05 PM   #11
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My thinking is that wenever you put on a black shirt on a hot day you'll start to get hot within the minute, but if you have a white shirt, it takes it a little while longer to get hot.
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Old 04-14-2009, 03:15 PM   #12
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Actually, whenever you put on a black shirt on a SUNNY day you'll start to get hot within the minute. It's the sun making you hot. However, wearing a black shirt on a hot day while standing in the shade doesn't get you any hotter than any other color shirt.

So, unless you drive your black painted engine around with no hood so the sun can warm the engine, painting it black will have little effect on actual engine temps.

But, what do I know. Ask the experts here like BEEF and RIDE.
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Old 04-14-2009, 06:35 PM   #13
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However, wearing a black shirt on a hot day while standing in the shade doesn't get you any hotter than any other color shirt.
I hate to call you out on a technicality but wearing a black shirt on a hot day while standing in the shade will get you slightly hotter. This is because black will absorb light and in the shade there is still light. Not as much as standing out of the shade of a tree but still there is light. Now if you were in a pitch black cave your statement would be true. Once again a slight technicality that probably makes me come across as a dick.

So now to the original poster ask yourself... is there enough light in your hood covered engine bay to merit painting it? I'm sure the differences are negligible.

Something else to discuss though is paint jobs on cars. Lately Flat Black or Satin Black paint jobs have been all the rage. Though aesthetically pleasing to the eye -- as they look real bad *** when you can actually keep dirt off of it -- flat black paint jobs absorb an incredible amount of light that a gloss coat would reflect. This light turns into heat and pretty much makes your car an oven compared to others. Make sure your AC it top notch!

Maybe a flat black hood would help you get what you're shooting for though.









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Old 04-14-2009, 06:56 PM   #14
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I was led to believe that black paint on an engine would radiate more heat to the atmosphere. An old friend who graduated from MIT with a degree in Theoretical Aerodynamics who raced Nissans in the 80s, so I guess he should know. One of the most brilliant people I have ever had the pleasure of meeting.

Now, for the purpose of mileage, you shoud try to retain any heat energy you can, so it would seem that there would be a logical argument for painting it with a white paint or even something with an insulating value.

I know one of the Insight hypermilers built a insulated cover for his engine. One of those hypermilers got 180 MG in a manual tranny Insight, averaging about 36 MPH.

Also the old Opel that got 300 + MPG a loooooong time ago had the engine covered with some kind of insulation, to keep it from cooling down when the motor was shut off.

regards
gary
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Old 04-15-2009, 05:20 AM   #15
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Too bad the black shirt doesn't radiate more heat to the atmosphere...white shirts stain when I'm outside doing yardwork.
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Old 04-15-2009, 05:37 AM   #16
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When it's hot I just dampen my T-shirt and let evaporative cooling keep me cool. When it dries out I just wet it again. I've done outdoor construction in greater than 90 degree weather with no problems (also drinking lots of water and using sunscreen). Of course some of you guys get hotter weather than that!
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Old 04-15-2009, 05:44 AM   #17
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Keeping fresh cool water on my clothes can help, but with me the water just gets hot really quickly and exacerbates the problem of sweat soaking my clothes and rubbing me the wrong way. Not much evaporation happens when humidity is 90%, maybe being further from the ocean you don't have that problem.
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Old 04-15-2009, 05:45 AM   #18
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Muggy days aren't real common here, it's true. I prefer water over sweat, if given the choice. My ex used to make wet T-shirt contest jokes when I did it.
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Old 04-15-2009, 08:24 AM   #19
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Sounds like some confusion here.

Gary is 100% correct. Yes, black does absorb heat very well. But, it is also the best heat-giver-offer. A quick google of "black body radiation" will probably give some insight.

Since the engine is essentially in the dark, there is no light to absorb as heat. However the black engine will radiate (give off heat) better, essentially making it cooler. That seems counter-productive since we've generally found results that indicate hotter is better.

However, the paint probably acts as a thermal insulator, offsetting the radiating effect (if that's what you are after).

-BC
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Old 04-15-2009, 09:25 AM   #20
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Gary is 100% correct. Yes, black does absorb heat very well. But, it is also the best heat-giver-offer. A quick google of "black body radiation" will probably give some insight.
i love technical jargon.
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