How to Color an Aluminum Radiator Black?

What paint, or other material, has been successfully used on aluminum radiators to color them black? Being a mechanical engineer with too many courses in thermodynamics I fully understand why the core should not be painted. I also know it is hard to get paint to stick to aluminum. I am trying to find a way to color at least the tanks black.

thanks,
Dave Christensen

The only way I know to get the tanks properly black is to use zinc chromate on them, then cover with black.

I would not coat the core.

I obtained a reproduction Marston aluminum rad and painted the top and side tanks black. Lasted the 18 years I used the car before I sold it.

I prepped the aluminum with PPG Alumiprep solution, then used PPG DP90 epoxy primer which is a pleasing semi mat black finish. Under the hood, I didn’t think UV deterioration would be a problem and it wasn’t but I could probably also have used a Duplicolor spray bomb in semi-gloss black acrylic lacquer.
DSCF0099

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Hi Dave, I recently had this same question, with regards to painting my CoolCat radiator end tanks. I got up with my Glasurit rep. He told me verbally nothing to it: Clean the aluminum with their metal prep. Epoxy prime. Then topcoat with urethane single stage or basecoat clearcoat.

This was a verbal. Just now I reviewed my written Glasurit tech manual. It basically confirms what he told me.

Black anodizing?

There is this:

How to Stain Aluminum Black | Shortcut Techniques (2023) (diyquickly.com)

No idea where one gets the black oxide pack.

Geez, I didn’t know any better and sprayed my CoolCat radiator with Krylon 10 years ago. Still looks fine.

Like others have suggested, I only painted the sides, tank and top.

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Hi, The easiest way to paint Aluminum is to first use a self-etching primer rattle can from most auto stores, then just paint rattle can black. There is no magic to it.

Regards,
Allen

I would avoid the use of any primer thicker than an acid wash for a radiator because a layer of primer, be it epoxy or etch, is a barrier to heat that can reduce the emissivity of the aluminum surface. Primer is proper advice for non-heat radiating components (or something you want to insulate.)

Similarly, a satin or flat black paint also increases emissivity over a gloss black paint. Remember why stoves are black, and why Lockheed painted the SR-71 Blackbird satin black! A true flat black would be best but might look pretty ugly after a bit of exposure to the environment. Could be the S2 black cam covers helped cool the XK engine just a bit more than the polished aluminum ones.

Granted, it probably isn’t that big a deal if it’s limited to the end tanks. I’d use the specialized radiator black paint though if possible and follow whatever steps the manufacturer of the paint recommends. Unlike painting our car bodies, the thinner the better!

Dave

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OEM condenser/radiator suppliers would do one of 2 things:

  1. degrease and spray paint on them
  2. degrease and a light coat of powder coat

Just a few points;

I’ve not had good luck with the spray cans of “radiator paint” sold by places like Eastwood or Giriot’s. These paints are very soft and so the finish is easily damaged. I think anodizing would look odd, and I’m not sure how it would work with welded seams. Powder coat requires heat to cure and so may not be the best choice, given that the radiator may be soldered (if copper) or brazed (if aluminum). While this is done at temperatures higher than powder coat, mistakes happen. Damage can be done just by thermal expansion at powder coat temperatures. A primer coat is an extra blanket of insulation. So if you must have black, the best bet is to thoroughly clean and paint a thin coat of flat or semi-flat paint. We’ve all seen old radiators and should know the paint was never lovely.

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It’s worth mentioning that Radtec have been around for 30+ years, and supply motor racing teams at a fairly high level.

They offer a powder coat option on all their radiators, and if you select that option, the core gets powder coated.

I realize this would not be recommended in a thermodynamics text book, but I like to believe that a company that supplies radiators to professional GT4 racing teams has done their homework on the real world effects of coating the core.

Fwiw when I had the radiator in my son’s Camaro recored I requested it back unpainted. I cleaned it thoroughly and painted it with semigloss rustoleum in a spray can. No primer. 10 years later when it was sold the paint looked as good as the day it was done. I plan to do the same with the e type if I ever get to that stage.

A radiator manufacturer has the processes to powder coat a radiator, even with epoxy, because those processes and equipment can carefully control the thickness of the coating to minimize insulation effects.

I am very skeptical that this can be achieved by most post-manufacture shops or at home. Not only does the thickness need to be controlled, but also the baking temperature.

Dave