Quadzilla Adrenaline - Optimal Engine Temperatures for Efficiency Optimal Coolant Temperature - 190℉  Factory thermostats set to either 190℉ or 192℉ are fine and will perform satisfactorily for most Quadzilla Adrenaline owners. For the people up north, it's possible to see coolant temperatures drop out below 180℉ because of the natural efficiency of the 24V and at idle the Cummins ISB tends to run cooler. When coolant temperatures start dropping the thermodynamics of the engine will sh