I agree. An aluminum radiator in contact with a dissimilar metal via the coolant, which is a weak electolyte, constitutes a galvanic cell.

If you "short" the dissimilar metals together, galvanic corrosion will be faster. Most radiators in my experience are electrically isolated from vehicle ground so the "short" doesn't happen.

See any basic chemistry text. The above concept is at about 300 years old.

Duke