Painting an engine: How does it affect cooling?

  • lgeis
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20 Jun 2010 21:01 #377157 by lgeis
Wouldn't painting a case, or especilly the cylinder & head assembly frustrate cooling to some extent?

I'd think the paint would produce some insulative effect...and that the unfinished (rought, unpolished) metal would cool much better.

Gal. 2:20!

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20 Jun 2010 21:34 #377173 by bountyhunter
Replied by bountyhunter on topic Painting an engine: How does it affect cooling?
Paint does reduce heat transmission between the metal and air, I don't know exacty how much. Can't be a huge effect as long as it's thin. With aluminum, you can anodize it to color it and not degrade heat transmission and if it's the right color, it may improve it very slightly.

1979 KZ-750 Twin

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21 Jun 2010 06:04 #377221 by bhardy501
Replied by bhardy501 on topic Painting an engine: How does it affect cooling?
I was considering painting my engine the same color I am going to paint my frame (Orange) and using polished covers on the sides and top or just sticking to black on the engine. I was curious as to what the effect would be on the heating. Would adding an oil cooler to a painted engine help with the heat issues?

1980 KZ1000B LTD

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21 Jun 2010 08:07 #377250 by Jack
Have had just about every type of paint on a wide variety of Z1/KZ motors over the last 36 years, never a problem.

79 KZ 1075 MKll
79 KZ 1500 MKll dragbike
Gone but not forgotten:
3 X 73 Z1's
1 X 74 Z1A
1 X 75 Z1B

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21 Jun 2010 09:19 #377269 by Bad Dad
bountyhunter wrote:

Paint does reduce heat transmission between the metal and air, I don't know exacty how much. Can't be a huge effect as long as it's thin. With aluminum, you can anodize it to color it and not degrade heat transmission and if it's the right color, it may improve it very slightly.


I've always heard that black transfers (or actually absorbs) heat the best.

76 KZ900LTD
82 GPz750R1
01 VULCAN 800A-CHOPPED
76 IRONHEAD-CHOPPED
77 RD 400 Cafe

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  • hugo
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21 Jun 2010 11:04 - 21 Jun 2010 11:06 #377281 by hugo
The effect of paint is practically negligible.

Most of the heat dissipation is done by convection. Air flowing throught the fins, not radiation.

Heat transfer from metal to paint is not very good, but heat transfer from metal to air is even poorer, so air can't keep up anyway even with the paint.


A black body is best dissipating and radiating heat, but only in the infrared spectrum not in the visible spectrum, (what it looks like to us), Nevertheless manufacturers paint engine in black when it comes to cosmetics, so when it comes to only radiation, (motorcycle is not moving), a black engine maybe be, theoretically, a little better dissipating heat. But obviously not enough to make manufacturers rush into painting all air cooled engines in black.
Last edit: 21 Jun 2010 11:06 by hugo.

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21 Jun 2010 11:09 - 21 Jun 2010 11:10 #377284 by bountyhunter
Replied by bountyhunter on topic Painting an engine: How does it affect cooling?
Bad Dad wrote:

bountyhunter wrote:

Paint does reduce heat transmission between the metal and air, I don't know exacty how much. Can't be a huge effect as long as it's thin. With aluminum, you can anodize it to color it and not degrade heat transmission and if it's the right color, it may improve it very slightly.


I've always heard that black transfers (or actually absorbs) heat the best.

Correct. There is a heat radiation effect called "black body radiation" which is enhanced by the color being darker, ie black is best for that effect. I suspect the effect is very small overall.

1979 KZ-750 Twin
Last edit: 21 Jun 2010 11:10 by bountyhunter.

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