How do I know if my thermostat is working properly?

Allow your car's engine to start. Do you know if the coolant flows? It shouldn't be flowing at this time because your car hasn't reached the operating temperature to cause the thermostat to open. The thermostat valve is open if you find the coolant flowing.Launch the engine of the car and let it inertia. Control the radiator neck to see if the cooler is sinking. At that time, it should not flow, because the car did not reach the operating temperature to get the thermostat open. If the cooler is found, this means that the thermostat valve is open.