How do you change thermostat 2005 mercury mountaineer?

To change the thermostat on a 2005 Mercury Mountaineer, first, ensure the engine is cool and disconnect the negative battery cable. Drain the coolant from the radiator, then remove the upper radiator hose connected to the thermostat housing. Unbolt the thermostat housing, replace the old thermostat with a new one (ensuring the gasket is in place), reassemble the housing and hose, refill the coolant, and reconnect the battery. Finally, start the engine and check for leaks.