2007 Lucerne CXL. and 1995 Lesabre currently, past 1973 Riviera, 1968 Riviera
Partially drain the cooling system.
Disconnect the Engine Coolant Temperature (ECT) sensor electrical connector.
Remove the ECT sensor.
Fig. ECT sensor location-3.8L engine
Replacement components must be the correct part number for the application. Components requiring the use of the thread locking compound, lubricants, corrosion inhibitors, or sealants are identified in the service procedure. Some replacement components may come with these coatings already applied. Do not use these coatings on components unless specified. These coatings can affect the final torque, which may affect the operation of the component. Use the correct torque specification when installing components in order to avoid damage.
Coat the threads with sealer GM P/N 12346004 (Canadian P/N 10953480) or equivalent.
Install the ECT sensor. Tighten the sensor to 18 ft. lbs. (25 Nm).
Connect the ECT sensor electrical connector.
Inspect and fill the cooling system as necessary.
Assuming you have the 3.8L, this is what you may be looking for, found on Autozone.