The debates already started it seems. I`ve had all kinds of the strangest stuff happen automotive wise but it`s taught me alot in the process. My belief is still a big external cooler on it and keep getting up. Sure I`ve heard about placing the tranny in "thermal shock" that will crack the case and yeah the world will end. Being I live in the deep south I know plenty about hot tempatures and humidity. But it gets plenty cold down here as well. In 2000, I bought a used, unknown number of miles TH350 lockup tranny. It had never been overhauled either. I installed a medium size external cooler and ran that tranny until 2007, placing over 70,000 hard miles on it and about 50 drag strip runs. The car spent time in the dead of winter in michigan in Feb. Never once did that tranny ever give me any issues.
I sold the tranny in 2008 and it`s still in use by the new owner.
Why I don`t like internal coolers:
1. Dead of winter, interstate, 70 mph. Radiator splits, coolant gone, being it`s winter and high speed, you can go a considerable distance before it runs hot. But, there`s no coolant in the radiator to cool the tranny fluid resulting in a cooked tranny. Exactly what happened on a 86 buick park avenue we used to have.
2. I would rather depend on 100 degree circulating air to cool tranny fluid over 180 degree coolant.
3. If the rad`s tranny cooler has never been flushed (like, who does this?) disconnect the upper and lower lines. Connect high pressure cleaner to the upper internal cooler inlet. or just blast it with a pressure washer. What comes out is white crap that`s really thick, it looks like cottage cheese.
This was what we found when we did my fathers radiator in his 98 GMC pickup that at that time had 100,000 miles on it. But I`ve did other Chevy trucks in those same year models with less miles and got the same results.
Now, not to say any of this can happen to anyone. But it`s happened to me and I do not perfer to go through it again. The inner cooler popping and coolant getting forced in the tranny is what happened to my 79 Z28 which caused it to puke fluid out of the dipstick, land on the header and smoke out the neighborhood where I had to sink down in the seat from the embarrassment. No thanks. Not signing up for that again as I hate to do work and spend a load of money on a transmission overhaul when I could have spent $50 on a external cooler and avoided it all.