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Old 03-08-2006, 05:43 AM
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Effects of paint on cooling components

Thanks all for the help on use of copper water lines. They are in now and pics will be on the Journal soon. A related theoretical question:

A friend of mine is on a pit crew for just the Indy 500 (last year they qualified 29 and were the first one out! LOL). Anyway, he says they have been painting the aluminum and steel cooling system components (including the aluminum radiator) with flat black paint to improve cooling.

I've read that cooper dissipates heat better than aluminum and no paint is better. No antifreeze helps even more. In my 9 second roadster, I replaced the standard tiny Scirocco (copper with plastic tanks) radiator with a fancy and expensive Griffin 4 core aluminum radiator. I was still at 220 degrees at the end of the quarter.

Any thoughts?

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Old 03-08-2006, 06:31 AM
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It is a well known fact that black dissipates heat faster.....

Horsepower means HEAT.........so 220 at the end of the run is not that bad....most engines make the most horsepower at 200 - 210 ......according to my friends at the Nascar engine shops......just up the road from my home....

Griffin Radiators is close by also......and I think they are vastly overated....I can get one at a discount ....thru a friend and I just bought a new Walker radiator for my 32 3W project( at full price...NO DISCOUNT )......brass and copper........Why ? ? ? ..... because I have one in my 32 Roadster and it works....great..... but all this is just my opinion and experiences.....
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Old 03-08-2006, 06:37 AM
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Effect of paint on cooling systems

I have a Walker on my '34 5-window and have no complaints either.
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Old 03-08-2006, 07:27 AM
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there is a special "radiator paint" marketed by Eastwood. This is an extremely thin paint...you get the black to radiate heat, and not thick enough to form a thermal barrier


or something like that
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Old 03-08-2006, 11:01 PM
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Most high performance and high dollar racing efforts are actually using "heat dispersant coating" which happens to be black. I've yet to see any sold retail, only applied by shops. Usually the same places that also apply stuff like ceramic coating to headers. This stuff is actually supposed to help the coated parts radiate heat, I know of nothing much else that has been proven to to any degree.
After some dyno experimenation, our shop settled on using spray can flat black lacquer for cylinder coating. You can color a cylinder (or a radiator) a nice black with only a very thin coat of it. On our runs we couldn't tell any real temperature differences between raw cylinders and black lacquer painted cylinders. It did seem the black engine might have run slightly cooler, but we weren't able to get appreciably different temperature readings. Of course we were really dynoing the bikes for other purposes of power readings not temps in particular. We did once run an engine with black enamel painted cylinders that ran measurably higher surface and oil temperatures. After bead blasting that paint off and re-running it with lacquer, the oil temperatures came down an average of 5 degrees F. The pyrometer went missing and we didn't get surface temps on that one though. We once tried a spray can of parts store "radiator paint"(been quite a while, maybe it was VHT?). Horrible nasty thick sticky stuff, an enamel based paint if I'm not mistaken. We couldn't throw it away fast enough. There may be other "radiator paints" such as Eastwoods that maybe don't completely suck. I also once had a radiator repaired at a shop and to finish off their work they apparently dunked it in the same nasty black crap as what came in that spray can. Yuck. Give me flat black lacquer.
Much as I would love to do a run with some dispersant stuff and see how it actually performs, I haven't and will have to rely on hearsay.
My conclusion would be that thermal coating would likely help, but may not be cost effective for you. A nice light coat of black lacqcuer won't hurt and possibly might be slightly beneficial.
I've always been a bit curious as to which is better, a naturally oxidized aluminum radiator (any one that is a couple of months old or more) or one that had received a light coat of black paint when new. I've never seen where anyone's tested this.

Last edited by GypsyR; 03-08-2006 at 11:09 PM.
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Old 03-09-2006, 05:09 AM
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Effect of paint on cooling systems

Thanks for taking the time to reply, folks. I think I will leave the cooper pipes uncoated as I sense that I will need every degree of cooling that I can get.
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Old 03-10-2006, 10:38 PM
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Heat transfer and cooling is a complicated topic but the principles are pretty easy to understand. Heat transfer occurs through three mechanisms; convection, conduction and radiation. Convection is very important in a water cooled car radiator. It refers to heat being transferred by fluids that flow past something at a different temperature. The flowing fluid transfers heat with that other item. The water inside the radiator tubes transfer heat from hot iron inside the engine and to the brass or aluminum tubes in the radiator through the mechanism of convection. Conduction or conductive heat transfer occurs in the metal of the engine block or tubes of the radiator. Heat is conducted from the hot side of the metal to the cold side. All materials have a specific conductivity - iron having the worst conductivity of any metal in a typical auto engine, then comes yellow brass, aluminum, and copper best of all. If the conductivity of iron is valued at 1.0, then the approximate relative conductivity of the other metals are yellow brass = 3, aluminum = 5, copper = 9. Other materials not used in autos for heat transfer but of interest are sterling silver with a relative conductivity just slight better than copper, and most surprisingly diamond wit a relative conductivity =50! A diamond radiator would have no cooling problems at all!!

You can see why copper is the best readily available material for radiators but if designed properly, aluminum is a good choice.

The final heat transfer mechanism is radiation which is where the black surface comes into play. Radiant heat transfer is easily understood by standing out in the sun. All of heat heat you feel is radiant heat. Anything of a higher temperature will radiate heat to something at a lower temperature. You at ~90R radiate heat to the cooler walls of your ~70F house. The surface condition is of paramount importance in radiant heat transfer. A highly polished pure white mirror surface is a good radiant heat restrictor - it radiates at the lowest rate. Conversely a perfectly black, perfectly flat (gloss-less) surface is the best radiator. That is why radiators are classically painted flat black and not a glossy light color. The problem is that paint is not a good conductor of heat even if it is a good radiator. A special paint with high conductive pigment like pure carbon black is a good compromise but whatever paint is used, thin coating is the key. Conduction and convection rule in a car radiator and the loss in conductive heat transfer far outweighs the small gain in radiant heat transfer if the paint is a good conductive insulator.
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Old 03-12-2006, 05:10 PM
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Effect of paint on cooling systems

Thank you, Professors GypsyR and Willys36. This is definately the web site to go to for answers.
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