JerryS.

The transmission uses its internal pump to pump transmission fluid through transmission lines through an external transmission cooler and back to the transmission. I don't know if your particular model uses a tranny cooler that is built into the radiator or a separate cooler. My 2015 GMC Sierra 1500 5.3L 4WD came with the separate tranny cooler. In the old days, transmissions were constantly cooled using this setup. In recent years, Chevy/GMC installed a transmission thermostat in these trucks to control the temperature of the transmission fluid inside the tranny. If I remember correctly, the factory thermostat is a 190 degree unit. The thermostat opens at 190 which means, depending on what you're doing with the truck, the tranny will tend to run hotter than that temperature setpoint. Many suspect the thermostat causes the transmission to run too hot for its own good and is detrimental over time. I purchased a transmission thermostat bypass kit and installed it. Easy install for my truck (30 minutes with no mess). My truck can display the transmission temperature on its information center display. The tranny temperature previously ran well over 190 degrees during the summer. It now runs around 160- 170 degrees with the bypass kit. I heard a rumor that Chevy/GMC now offers an optional 150 degree transmission thermostat, but never bothered to confirm since I'm satisfied with the bypass kit.