Quite a few cars seem to go for a long time without tranny meltdown. If so, lucky for those guys. My tranny has been apart twice in twelve months, I am not in a hot climate, nor am I a hard driver. Not so lucky.
When my car was first fixed to have four forwards, I drove in D, the brake band went, followed by the clutches. This time, to be sure to be sure, I am using 3 for town driving, and have an extra cooler installed.
Trevor is right on first principles regards heat. These trannies tend to change up quick, attain and hold D. When asked for power, if the TCU does not select 3 or lower, the T/C is doing all the multiplying, and is creating lots of heat in the oil. This will have worst effect where the temp peaks are held for long periods, such as long hillclimbs, or continuous town driving. Excessive heat will "kill" the oil over time, and cook the friction material. People who flush and change their oil very often offset this, and using special hi-temp synthetic is also a help.
I also suspect when you run two coolers or an additional big one [mine is 19,000 lbs rated] the ATF may be overcooled as a result. This may explain why Kuoh's does not show additional heat using D, if he has an extra cooler. My car seems to be about 2 mpg more thirsty than when I had no extra cooler, and I am putting this down to the oil not being warmed up a lot, particularly as I use the AC most of the time. The AC fan is pulling air through the new cooler and the OE one all the time.
To answer RC's first question, a '96 car does not have the troublesome mesh in the cooler, which is attributed to hastening the demise of the earlier cars' transmissions. It is likely if you put in an additional "helper" cooler, you can drive in any gear you like without worry, assuming you don't drag race it everywhere.
Joe
