Xtra Cool Transmission Cooler Thermal Bypass Valve Upgrade 13-18 Ram XDPReplace the problematic factory thermal bypass valve in your 2013 2018 Dodge Ram 6. 7L Diesel before it causes catastrophic failure with the XDP Xtra Cool Transmission Cooler Thermal Bypass Valve Upgrade XD343. The OE thermal bypass valve is designed to route bypass the transmission cooler in cold temperatures in order to bring the transmission up to operating temperature faster. Unfortunately, the bimetallic valve commonly fails in the closed