You have a aluminum tube and fin oil cooler.

What will dissipate more heat:

1. Leaving it alone (aluminum finish)
2. Painting it black. (black should dissipate heat better, but does the layer of paint act like an insulator.......)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

black paint will be slity less efficeint. I can get A/C evaporators (home) in ethier one. The black lasts longer but is slity less efficeint.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

My 2 cents.
Air insulate, paint without "air" should not do it.

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Lasse

Signet -66 225
Holley 600 Offy-5270 Dutra Dual,regrind. cam 272 0,420 110, head shaved 0.100 slight.ported
MSD6A
A904
7 1/4 3.23

Unpainted = better.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I wouldn't polish it or paint it. Make sure it gets plenty of airflow to it and through it. I would leave an aluminum radiator or cooler plain.
Don't bet too much on that. In radiation, that can be part of the equation, but only part. What kind of paint? How thick? Emissivity? Believe me, not every black paint is good at radiating.

The primary means of transferring heat in this situation is convection, not radiation. Convection is about temperature differences, fluid flow, and thermal properties of the materials involved, not color.

Radiation is about temperature differences and emissivity. Color can be part of emissivity, but there are a lot of factors that are more important - material, surface condition, geometry, and temperature.
Yes, paint can insulate.

There are probably charts somewhere of the emissivities and other thermal properties of various paints at certain thicknesses and temperatures, but I don't have them.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

If its corrosion protection that concerns you, I use a light silicone spray on my radiator it seems to help to prevent my fins from rotting out and makes it easier to clean.