I sort of subscribe to if your gonna build something make it to a minimum of daily driver standards. May cost more for somethings but you will encounter less problems down the road.

You also have to think about geographic location. You can get some big temperature swings. Last week here in Saskatchewan. It was -5'C (23'F) in the morning and reached a high of 18'C (64'F) in the afternoon. Up a external cooler bypass is required. When it gets so cold that the fluid doesn't move through the second cooler, a pressure valve opens and the system runs completely on the radiator cooler until the fluid gets hot enough. On the freezing -35'C winter days up here you could literally cook your transmission if you added a huge tranny cooler and didn't have a bypass.

My truck will see winter duty.

 

I have followed this thread carefully because I want to understand for future reference. So based on personal experience,
the info in this thread, as well as info gathered from other places, here are my conclusions:

1- Radiator transmission cooler only = good
This is based mostly on my personal experiences with a few 200,000 mile plus vehicles with no transmission problems. Mostly highway miles, no towing, no hard driving (ok very little hard driving)

2- Radiator transmission cooler and external / auxiliary cooler = better
A must have for for towing / heavy hauling (need to add a thermostat / external cooler bypass in cold climates)

3-External / auxiliary cooler only = depends
Live in a warm climate or only drive during the summer = great (make sure cooler has proper airflow)
Live in a cold climate = bad (fluid will not reach operating temp?)

So please tell me what you think about these conclusions. Am I missing something?

 

I put my thoughts, few as they are, in the text.

 

I'd change #2 conclusion from a blanket "better" to "if needed for extreme use conditions, not good for ordinary driving can overcool".
And the conclusion to #3 to "never a good idea". Better than nothing, would be the best I'd give it. No automatic tranny specialist would ever endorse this arrangement unless he expected to be the one you end up paying to rebuild it for you. No moderation/control of the fluid temp, cannot possibly set up to cool the proper amount for the varying conditions we encounter every day. Take this example of one average trip: Good temp on a moderate day driving at steady 55 MPH, increase speed to 70 MPH and can overheat or overcool ???? Pull off the highway into stop and go traffic, fluid overheats. Attach a trailer, fluid overheats. Day turns to very cool night, fluid overcooled. Starts to rain, intercooler bathed with a continuous stream of water, fluid overcools. You would need to install a bank of intercoolers/fans/thermostats and or computerized valves/sensors to maintain the fluid temp in it's design range on just this one average trip, and if you are honest there is no such thing as an average trip.
My 1/2T pickup came from the factory with a 10K towing capacity package. Did they add an air fluid intercooler for the tranny for this severe use? Nope! They put in a larger radiator.
If this were a good idea no one would need AC/heat to heat/cool their house/vehicle. Just put a large intercooler outside and blow the inside air thru it. Laughable right? but this "option" is based on the same principle.

 

Thanks for the input guys. Based on vehicle usage one of the first two options seems like the best.

AX while it's true that 95 degree outside air will not cool a 95 degree house, 95 degree outside air will offer some cooling for 200+ degree transmission fluid (with the proper amount of surface area and airflow). I agree however that the radiator based cooler helps to maintain a more consistent trans fluid temp.

With all that being said I like the radiator based cooler with an added aux cooler when necessary. Throw in a temp gauge. Use a thermostat/bypass on the aux cooler if trans fluid temps get too low.

Hope I have drawn the right conclusions here but if not at least I can do my part to stimulate the economy when my transmission needs a rebuild.