[SparkyRnD]

if the whole radiator was copper, it would have a single even dissipation rate for cooling, and would be better. but when mixed with brass, they have different cooling rates. That is one reason why the aluminum is more efficient, is that it heats up and cools at a single even rate. That also leads to less stress cracks, as you don't have two dissimilar metals heating and cooling at different rates that are in contact with one another.