With the engine cold, check the coolant level in both the radiator and the overflow bottle. Top off the coolant so the temperature sending unit stays in contact with coolant when the heater or defrost is turned on.
The owner of a 2000 Dodge Caravan said that after adding coolant, the temperature gauge drops into the cool range only when defrost or heat is turned on. The expert explained that the coolant level falls when the heater is used, so the temperature sending unit loses contact with the coolant and the gauge reads incorrectly. The advice was to check the cold coolant level in the radiator and overflow and top it off.
