I read the bypass is so the trucks get a few thousands more mpg by warming up the transmission sooner and that makes the EPA happy. I’m no expert but I’ve been into a couple of automatics and I’ve had a lot of them built and no transmission man has ever told me that it’s possible to over cool an automatic… Unless maybe you’re in Minot or Fairbanks. Craig
The friction material on your clutches wears less when the trans is warmer, even hotter.
Ford now has their transmissions running at the same temp as the engine coolant. For a while now. ZF told them to.
Metal likes heat to a certain extent. 500 degrees is bad but, in general, the hotter you can run it, the longer it will last and the more power it will put out in an engine. In a trans, the less it will wear.
Heat is energy. Energy is heat.
The problem is...... The working parts of the trans (and engine) can take the heat but the gaskets, seals, etc can not.
Ask any machinist. Trying to turn hot metal is a struggle. Gotta keep it cold in order to work it. Too hot and it won't do squat.
As to the EPA?? Whatever.
I know that my truck gets lousy fuel economy until the engine and trans get nice and toasty. I mean, heat-soaked toasty. On the highway, my first 150 miles kinda sucks. After that, I'm doing pretty good, mileage-wise.
Over-heating is bad, real bad. But right behind it is too cold believe it or else.