The cooler in the radiator is often misunderstood. The heat exchanger in the radiator is a liquid to liquid type so it is far more efficient at transferring heat then an air to liquid cooler like the auxiliary or aftermarket coolers, even for its small size the radiator cooler alone does a ok job of keeping trans temps down on a stock XJ under normal driving conditions. Also it does very little to heat the fluid, it is on the cold side of the radiator, the fluid coming out of the transmission is almost always hotter than the cold side of the radiator, even on a cold day before the engine is warmed up. The correct way to plumb an aftermarket cooler is in after the radiator, that is how its done from the factory if you have the auxiliary cooler, and it is how other auto manufactures do it as well.