P0128 Code: Coolant thermostat -coolant temperature below thermostat regulating temperature


Jeep Owner
Threw a P0128 code just cruising around town. Deleted code and checked engine coolant. My fluid has always shown just a small amount just visible at bottom of reservoir, which was the case. Had mechanic tell me he had had to replace abnormal amount of engine coolant thermostats on the JK. Mine is a 2013 with 45K miles. So on my next adventure noticed I had to kick heater up to above normal heat to be comfortable. Coming off mountain on paved road noticed my engine temp gage had dropped about 25% below the normal straight-up position. I was coasting with no load on engine other than engine braking. Temp was about 40 f outside. No engine code thrown. Before I blindly replace thermostat was curious if anyone had comments. Thanks!