How do you change the thermostat on a 1998 ford expedition 4.6?

To change the thermostat on a 1998 Ford Expedition 4.6, start by ensuring the engine is cool and disconnect the negative battery cable. Drain the coolant from the radiator, then locate the thermostat housing, which is typically near the engine. Remove the bolts securing the housing, take out the old thermostat, replace it with a new one (making sure the gasket is properly seated), and reassemble everything. Finally, refill the coolant, reconnect the battery, and check for leaks.