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As Dan inched our 6.7L F-350 onto the trailer, the October sun beat down onto the black asphalt. It wasn't even 11:00AM and the thermometer read almost 80°F; hot for October in Delaware, but perfect for transmission cooler testing. I climbed into our 6.0L F-250 follow vehicle while Dan cranked down the straps on the trailer and we set out for an afternoon filled with hills and valleys.

Our last look at the 6.4L Powerstroke transmission cooler revealed something a bit out of the ordinary for our blogs. Instead of highlighting all the failures of the stock transmission cooler, we shared that there really aren't many, yet. Yes, the stock 6.4L trans cooler is good enough. Good enough for a stock truck.

What defines a limit? In the English language, a limit is "a restriction on the size or amount of something permissible or possible." In practice, however, limits are not always as rigid. Anybody who's ever mastered a sport or skill will tell you, limits are made to be pushed and broken. A limit is only as defined as one's willingness to accept it. In the automotive industry, limits are often found by exceeding them. We push our cars and trucks until flaws appear, then step back and find a way to make them better.

Physics tells us that almost everything has limits, whether or not we've found them yet. Air at a certain temperature can only absorb so much heat energy, and transmission fluid loses its ability to lubricate beyond a specified temperature. Add a transmission cooler between the two, and you have hundreds of variables that will decide the limits of what's possible for your truck. In the case of the Ford 6.4L Powerstroke, the limits have yet to be defined.