Copper vs. Aluminum

There's more to heat transfer than just the conductivity of the material. With a vehicle radiator there's the heat exchange of the fluid to the tubes, and then the conduction of the heat through the tubes and the finsm and finally the heat exhange with air. The last is largely convective and will involve both the tubes and the fins. I remember being surprised in one class excersize that the fins can be designed so that they will make the heat exchange worse! IIRC that was a passive convection excersize. My point is only that aluminum's disadvantages can be largely overcome in this particular regard. That doesn't make the observation of the differences in coduction any less interesting - its certainly an important factor