GEEZThis is for all of you to understand how the trans works. Ford had installed the bypass before the superduty. Yes It will open if the cooler becomesplugged.But if your cooler is plugged then the trans has already failed! Ford used the bypass on the superduty to warm the fluid up on the early years with no rad coolers. I have seen a lot of posts about not using rad cooling. You must use engine temp to bring trans fluid to operating temp. The more even the trans fluid stays the longer the life of the trans.
The bypass is not there to warm the fluid. It is there to provide lubricant to the rear of the transmission in case there is a flow restriction thru the coolers, for whatever reason.
The radiator cooler is not there to bring the fluid to operating temp. It is there to cool the fluid.