How do you change a thermostat on a 2002 Mercury Sable?

To change the thermostat on a 2002 Mercury Sable, first ensure the engine is cool, then disconnect the negative battery cable. Drain the coolant from the radiator, remove the upper radiator hose from the thermostat housing, and unbolt the thermostat housing. Replace the old thermostat with a new one, ensuring it's oriented correctly, reassemble the housing, reconnect the hose, refill the coolant, and finally reconnect the battery.