[oil pan 4]

Originally Posted by jeff88

What about a thermostat like this? It bypasses the cooler until temps reach 180 at which point it opens, allowing the fluid to run through the cooler.

Derale 13011 Fluid Control Thermostat Kit

Is 180* too hot for the trans?

That is precisely what I used and it did not work. Save your money.

I figure the best way to keep the transmission at the ideal temperature is to run 2 systems. A factory system (at least for GM) where the cooler acts more like a heater or heat exchanger with the engine coolant and a straight up air to oil cooler that puts a large amount of fluid surface area in contact with air, for use when towing or when its Texas/New mexico hot out.

Then the 2 systems would be manually opened or closed or both opened.
An electronic system would work by opening a normally closed heat exchanger/heater when the trans is cold. Then as it warms the cooler side, which is normally open and is energized and held closed during warm up opens. During normal operation in summer the heater constantly flows and the A/O cooler occasionally opens up.
In winter the heater always flows and the A/O cooler almost never opens.
Then when you hook up a 10k GTW trailer in the middle of summer and really warm up the transmission the "transmission heater" actually closes and everything runs through the A/O cooler. Or you can manually flip it to cool only.
If the system fails and goes non functional the "transmission heater" section closes (the reason for the normally closed valve) and the Air/Oil cooler fails open (the reason the A/O cooler has a normally open valve) and the transmission runs really cold.