The 12-valve first-gen Cummins in your Ram is considered one of the best diesel engines ever produced, and for good reason. Fuel efficiency, torque, and simplicity are just a few characteristics that give the Cummins its stellar reputation. We're huge fans of the Cummins engine, which is why we've developed a low-temperature thermostat for the 1989-1993 5.9L 12v Cummins. This Mishimoto thermostat activates at a lower temperature (174.2°F) compared to the factory thermostat (180°F). By lowering the activation temperature, coolant flows through the radiator earlier, maintaining lower fluid temperatures. The Mishimoto low-temperature thermostat is ideal for vehicles in warmer climates, or for use in vehicles experiencing extreme driving/towing conditions. This thermostat includes a high-quality replacement gasket and our signature Mishimoto Lifetime Warranty.