A thermostat regulates the flow of coolant into the engine based on the engine's operating temperature. If the thermostat is not working properly (stuck open or closed), it can cause the engine to overheat and do permanent damage. Replacing the thermostat on the 2005 Buick LeSabre is relatively simple by comparison, since you do not have to drain the engine coolant and can access it from the engine compartment.
Open the hood of the 2005 Buick LeSabre. Trace the radiator hose to the point where it connects to the thermostat cover, on top of the intake manifold.2
Press the tabs of the radiator hose clamp together, using pliers. Slide the hose clamp off the connection so that you can remove the hose from the thermostat. Pull the hose off of the thermostat.3
Remove the thermostat cover bolts using a wrench. Remove the thermostat cover.4
Clean the mounting surface of both the thermostat cover and the intake manifold with a flat object such as a spackle tool. Discard the remnants of the old gasket.5
Extract the thermostat from within the intake manifold and discard it. Replace the old thermostat with a new thermostat designed to fit the 2005 Buick LeSabre.6
Lay the new thermostat cover gasket on the mounting surface of the intake manifold. Place the thermostat cover over it and tighten the bolts to secure it in place.7
Replace the radiator hose on the thermostat cover. Press the tabs of the hose clamp and slide the clamp back onto the connection.