Follow the top radiator hose down. It will connect to the engine. At the point that it connects to the engine is where the thermostat is located. This thermostat cover will have two bolts. Some of the 3800 engines have a temp sensor in the housing. You will not have to mess with the sensor. The housing will have 2 bolts that hold it on. Remove the two bolts and the housing will lift off. And the thermostat will be under the housing. Replace the thermostat. And reinstall the housing.