Cool Aluminum Cold Copper

I see everybody using aluminum radiators.
How do they stay cool? Copper, as
I am sure you know, transfers heat better
than aluminum. What am I missing?

You are correct about the Cu vs. Al heat
transfer specs. What you are missing,
though, is that radiators are not, and
never were, (at least since the 1930s),
copper. Copper is too soft to handle
any pressure. Radiators were brass, and
brass doesn’t conduct heat as well as
aluminum, typical numbers are 164 BTU/
hr. ft °F, vs. 126 BTU/hr. ft °F for a typical
aluminum alloy.
Aluminum, being stronger, allows wider
tubes, increasing surface area, and can
handle much higher pressures. Brass
does have some advantages: It is easily
repaired (solder).