How do you replace thermostat housing in a mercury mountaineer?

To replace the thermostat housing in a Mercury Mountaineer, first, ensure the engine is cool and disconnect the negative battery terminal. Drain the coolant and remove the hoses connected to the thermostat housing. Unbolt the housing from the engine, clean the mating surfaces, and install the new housing with a new gasket. Reconnect the hoses, refill the coolant, and reconnect the battery terminal before starting the engine to check for leaks.