The thermostat in a 2013 dodge avenger equipped with a 3.6 liter engine can be found under hood to the left of the engine below the oil reservoir on the passenger side of the engine bay. the thermostat is responsible for managing the amount of coolant circulated through the motor via sensors that monitor the temp of the vehicle and its fluids. when the car is switched off and cool, the thermostat will be closed. when the vehicle reaches operating temps, it will open to allow coolant to flow between the radiator and the motor. if it becomes "stuck" open due to failure, the car's gauges will become erratic, overheating will occur and coolant leaks may develop.
On the 2013 dodge avenger 3.6 the thermostat is located under the housing near the water pump on the cylinder head.