Why must a car radiator have a high corrosion resistance?

Car radiators generally don't have a high corrosion resistance.

Lately, radiators are being made from aluminum. Aluminum 'rots' quickly in the presence of other metals and a good electrolyte. For that reason, it is important to use a coolant in the recommend concentration that is formulated to prevent this. It is an extremely good idea to change the coolant every two years because the chemical additives that protect and lubricate become depleted.