This is a simple explanation of the physics involved, which is emissivity and heat transfer. https://www.reddit.com/r/explainlik.../eli5_why_does_painting_something_flat_black/
Here's more, if you really want to read up on it. The main sentence as far as this discussion goes is: "The main exception to this is shiny metal surfaces, which have low emissivities both in the visible wavelengths and in the far infrared. Such surfaces can be used to reduce heat transfer in both directions; an example of this is the multi-layer insulation used to insulate spacecraft." https://en.wikipedia.org/wiki/Thermal_radiation I think Squirrel is right, that it probably makes little difference. But as I pointed out above, it certainly doesn't hurt to paint the radiator black.
I took a look today at Home Depot for a semi-gloss high heat black... No dice. As I mentioned, I have used flat black and then done a shellac clear and it looks amazing - like it was painted in 1935. But shellac won't work on a radiator of course. This radiator paint mentions above is probly an online order? Member: Rochester Street Rods - Est. 1970 http://www.rochesterstreetrods.org CrossMembers Car Club - Hebrews 12:2 http://www.crossmemberscc.com
I don't think it has to be a special paint, it doesn't get that hot. I've used regular old Rustoleum spray paint and it holds up fine.
I just used normal gloss black $4 a can spray paint on the radiators I've painted, it works, although it's probably not perfect. I'm not into perfect, so no big deal. It's good enough to go in the magazine
Yea I don't do perfect either lol it would stick out too much as the rest of the car and the drive are far from perfect I figure it gets 200°f plus right? Regular paint can handle that? Member: Rochester Street Rods - Est. 1970 http://www.rochesterstreetrods.org CrossMembers Car Club - Hebrews 12:2 http://www.crossmemberscc.com
That simplifies things. Thanks for the talk guys Member: Rochester Street Rods - Est. 1970 http://www.rochesterstreetrods.org CrossMembers Car Club - Hebrews 12:2 http://www.crossmemberscc.com
Seems to me that the first thing is to determine if a automotive radiator displaces its heat to the air by radiation or conduction. If by radiation, painting it black would be just fine. However, an automobile radiator obviously does not transfer but a tiny % of the heat into the atmosphere by radiation. They do it by conduction. The air molecules in contact with the warmer surface [fins and tubes] take up the heat. The 'exchange rate' is dependent on a lot of factors but the amount that can be attributed to infra red radiation will not be large. If radiators 'radiated' the bulk of its heat [and conduction was not how they operate] a fan would not be necessary. So it seem to me, in as much as aluminum/copper and etc., conduct heat a whale of a lot better than dried paint, that painting a radiator is contraindicated if a marginal situation exists. No problem with a current unpainted aluminum radiator? Go ahead and paint it and see if everything is still fine this summer. If a guy has no idea about how a new build is going to work cooling wise, it would seem wise to hold off until the system has been operation for a while.
Car has over 1,000 miles on it. Has a stock radiator (6cyl) and it has a hard time cooling the v8. Also doesn't have a built in trans cooked. I am very happy about getting this new one as a gift for many reason but I can't just throw it in as it means a short pump to fit which means new pulleys and alternator brackets; neither of which I have laying around So I already know it has an issue but that's with a way smaller radiator Member: Rochester Street Rods - Est. 1970 http://www.rochesterstreetrods.org CrossMembers Car Club - Hebrews 12:2 http://www.crossmemberscc.com
I'm doing a '49 Fleetline for a friend right now and had the same experience... Was overheating with the stock radiator and long pump with a small fan, no shroud, so we're in the middle of putting a short pump and pulleys, 17" fan, shroud and a new aluminum radiator. Should have it ready this week. We were just discussing whether to paint it or not.
Conduction would be the process of heat transfer through the metal of the radiator itself, radiation is the process of heat transfer from the radiator to the atmosphere.
When you finally get it painted and dried, cut two pieces of cardboard the size of the core and put one on front and back. The aluminum fins bend very easy and getting it in the car without hitting at least one side is tough. The cardboard will keep them nice and straight and once in place, you easily pull the out. Joe
Coal burning pot belly stoves have been painted dull black forever for a good reason. The Italians did a scientific test in the 30's or 40's (don't remember which , I read it in the 60's ) to determine which color dissipated heat best on racing motorcycles and flat black was found best.
I've thought about having my aluminum radiator anodized flat black before, but always wondered if the anodizing process would affect heat flow. Used to have access to anodizing equipment a long time ago, but the EPA put the kabosh on that in the 80's. The only real advantage I see would be the thin even coat, otherwise should be the same as painting one. Anybody ever tried it? Posted using the Full Custom H.A.M.B. App!
The best reason to paint it black is so it 'disappears'. As for all the other fancy words I can't spell or pronounce, I really don't give a damn.
Automotive radiators transfer heat to air primarily via conduction and forced convection. The conductive portion is transfer of heat from the fluid thru the metal itself, which is why radiators are made as thin as possible within the limits of durability. Thicker material has a longer conductive path which would slow the heat transfer from the interior to the exterior of the radiator, and the heat has to reach the exterior surface before it can be carried away by air flow. The heat is removed from the surface of the radiator via forced convection. Air moves across the surfaces by the combination of the fan or the movement of the vehicle down the road, or both, depending on speed. The theory of black body radiation would indicate greater radiant heat transfer for a black painted radiator, but as previously stated by modelabc, only an extremely small percentage of the heat transfer is via radiation. Conversely, the coat of paint impedes conductive transfer thru the metal to some degree, so in that respect the paint has a negative effect on heat transfer. My guess is that the overall effect of paint is slightly negative, but the difference wouldn't be enough to make a difference in whether or not the radiator will cool adequately.
Anodizing wouldn't be a good idea. Anodizing converts the surface to aluminum oxide which has much higher resistance to conductive heat transfer as compared to bare or even painted aluminum. The radiator would likely still cool just fine assuming it had adequate cooling capacity prior to anodizing, but the process definitely would not be an enhancement to the radiator's cooling capacity.
You got the first part of the sentence correct. The hot water heats the metal of the radiator....conduction. But it's also 100% true that it's also conduction that gets the heat from the metal into the air; radiation plays a very minimal part in the process. Radiation of heat will take place through a vacuum. Such as from the sun. As long as the heat source can 'see' your hands the infra red end of the spectrum will warm them even if the flame is behind glass. If you stand near a window and the sun is shining you can feel its warmth. But that is NOT how a radiator works! It is absolutely true that it works by CONDUCTION of the heat from the fins/tubes of the radiator to the blast of air supplied by the speed of the auto and/or the powered fan. So don't paint them because dried paint is a lousy conductor!
The way I was taught it, the radiative effect of the radiating surface depends on the frequency of the radiation. Colour is more important at frequencies higher in the IR band; texture is more important at lower frequencies. At the sort of far-IR frequencies a car radiator radiates, colour doesn't matter much. Matt surfaces of any colour are good, though, the coarser the better: not only do they radiate far-IR better, they also have a greater specific area at the microscopic level.
I am considering painting my aluminum rad in my RPU using the black spray paint that they sell for repainting gas barbeques.
You guys do realize that you are likely talking about 5-7º, under controlled laboratory conditions, right? Unless you are always driving in that lab, painted, not painted, glossy, or matte, you cannot generate scientifically gathered statistically significant data. Drive more, post less.
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