The radiator also stabilizes the tranny oil temperature. Warms it in cold weather, cools it in the summer, keeping it around the 200 degree area. A lot of tranny rebuilders do not like to warrenty their trannies if you use the cooler without cleaning it out, or use a filter in the cooler lines. When a tranny goes south, all those metal particles go through the whole unit, including the tranny cooler(s).