How do you change a thermostat on a 1995 Cadillac sedan deville with nortstar?

To change the thermostat on a 1995 Cadillac Sedan DeVille with a Northstar engine, first, ensure the engine is cool and disconnect the battery. Drain the coolant from the radiator, then remove the upper radiator hose and the thermostat housing, which is typically held by bolts. Replace the old thermostat with a new one, ensuring the gasket is properly seated, and reassemble by reversing the steps. Finally, refill the coolant and check for leaks after starting the engine.