Please note: I edited my earlier post, since I had the flow directions backwards. Haven't gotten much sleep in the past week, and I gave the directions for the best way to heat the tranny fluid, not the best way to cool it. The current information is accurate.
Anyway, if you're going to use the radiator cooler, and an external cooler, you should route the supply to the top of the radiator, then the bottom of the radiator to the external cooler, then the other external cooler connection to the return line to the transmission.
Several performance transmission places which I've talked to, have recommended not using the radiator cooler, at all. There is a valid concern, since it guarantees that the tranny fluid will always be dependant on the engine coolant temperature, when we really want the tranny fluid to be cooler, if we can make it happen. I'm shooting from memory here, but I believe that the desired temp for tranny fluid is really in the 160-180 range, while the engine should operate in the 180-200 range. Exposing the already-heated (above 200 degrees) tranny fluid to 180-200 degree coolant, means that it will never dip below the coolant temperature. Actually, it will be significantly warmer, since cooling depends on efficiency, which is always less than 100%, and goes down as the temperature gap gets smaller.
The fluid-to-air cooler isn't as efficient as the fluid-to-coolant cooler, but the temperature gap between the ambient air and the tranny fluid is much larger than the temperature gap between the coolant and the tranny fluid.
Now, using both adds another issue, since the external cooler can reduce the temperature below the coolant (assuming the external cooler is after the radiator cooler, like I suggested above), but the smaller temperature gap between the semi-cooled tranny fluid and the ambient air will reduce the efficiency of the cooler.
In other words, a large external cooler, without the radiator cooler, is probably better than the radiator cooler and a small external cooler.
Joe
