Does painting an aluminium radiator black improve cooling?

No. The paint adds an insulating layer that slightly degrades the exchange. Radiation is marginal compared to forced convection in a car radiator.

Why were old radiators black?

Copper/brass cores oxidise with coloured oxides. The black paint mainly served as protection and surface uniformity, not to improve the exchange.

Does copper really conduct better than aluminium in a radiator?

The real “copper” core incorporates brass and brazing, which reduces the effective conductivity (~160 W/m·K). A modern brazed aluminium core is often ~170–180 W/m·K.

Aluminium Black Series radiator Mespiecesauto

Aluminium Black Series radiator: the false good idea

Aluminium radiators painted black — nicely named Black Series — promise a “period” look. But thermally, adding a coat of paint is a nonsense.

Why were pre-1990 radiators black?

The cores were made of copper/brass because the manufacture and assembly of aluminium were still difficult and costly. The soft soldering (tin/lead) made copper easy to produce and repair.

Copper, the better conductor?

Pure copper shows ~385 W/m·K, aluminium ~220–235 W/m·K. But a real “copper” core is in fact copper + brass (brass ≈ 100–150 W/m·K), with brazed joints that add thermal resistance.

In practice, the effective conductivity of a copper/brass core is typically around ~160 W/m·K, very close to a modern aluminium core ~170–180 W/m·K (brazed aluminium tubes + fins, high thermal continuity).

The role of the black paint

Copper oxidises quickly: Cu₂O red/brown (≈ 70 W/m·K) → CuO black (≈ 20 W/m·K) → verdigris (almost insulating). This coloured oxidation degrades the thermal exchange. The black paint therefore served above all for protection. The gain in radiation is negligible: in a car radiator, ~95 % of the transfer passes through forced convection (fan/speed), not through radiation.

And aluminium?

Aluminium also oxidises, but forms a very thin white layer (a few nm to µm), stable and protective. Its thermal impact is negligible and barely changes over time.
Painting an aluminium core black amounts to adding an insulating layer which degrades the efficiency, with no thermal benefit, or any other advantage over its lifespan. Work published in “Manufacturing Science and Technology – Investigation on Suitability of Aluminium to Copper in radiator” concludes there is no seriousness in painting an aluminium radiator.

Technical choice > marketing choice

At Mespiecesauto, the priority remains the function : a radiator must cool. The Black Series may perhaps be visually flattering, but thermally counterproductive. Keeping the aluminium bare means preserving performance.

Discover our aluminium radiators for Alpine, Renault, Peugeot, Alfa Romeo

For information about a development of an aluminium radiator, contact us

Note: Typical values given for indication (range of alloys, geometries and processes). Overall efficiency also depends on fin density, pressure losses and brazing quality.

Reference: A.K. Dubey, “Investigation on Suitability of Aluminium to Copper in a Radiator”,
Manufacturing Science and Technology, 3(1):16–23, 2015.

Benjamin, Founder of Mespiecesauto
Engineer passionate about automotive reverse engineering.
The blog is here to demystify certain established technical facts.