As many of you know, most of our '04-08 F-150s have a temperature controlled bypass valve for the transmission that bypasses the coolers until the trans oil temp reaches about 185 degrees (this is according to some Ford documentation I just received). The unit looks like a square block and is in the cooler lines near where the engine meets the bellhousing. The idea behind it is to keep the trans from overcooling. Also, the torque converter does not lock up until trans oil temp reaches about 85 degrees, and Ford wants to hasten than point.
I can think of reasons to like this device and I can think of reasons not to. A tranny rebuilder on another FTE board claims this unit is notoriously unreliable and when it fails, it more or less permanently bypasses the coolers and leaves the trans vulnerable to overheating. I can see how that could happen.
Thing is, thus far, I'm not hearing much from other sources to back up his statements. Not calling him a "laar" because his particular experience could lead him to that conclusion. I'm looking for broader evidence, so if anyone out there has a story on this device to relate, or knows someone who does, would love to hear. In the meantime, I am contacting other sources to work up my data.