[Bad Moon]

I believe all 3 brands work the same as my Silverado/Duramax/Allison. The transmission sends the fluid first to a heat exchanger in the radiator, then to a cooler then back to the sump. As your engine produces more heat (for example pulling your 5er up a long grade) it heats up the coolant in the radiator and consequently the trans fluid that runs through it. I can’t believe the newer trucks don’t have a digital trans temp like my 2007.5 has. I have only seen my trans temps go as high as 215 in extreme conditions (high ambient, high altitude and long steep grades). Allison’s are tolerant to fluid temps over 300 degrees, so no worries. My engine coolant temp gauge is analog, and they are notoriously innacurate, although on the conservative side (200 indicated is actually closer to 180). The advice above for getting the iPad app to read engine parameters is good, although my dash is getting crowded with electronics!