2. Open the hood of the vehicle.
3. Locate the thermostat housing. On the 1999 Nissan Sentra, the thermostat housing is located on the front of the engine, on the left side of the engine compartment. It is a round, black plastic housing with a single bolt in the center.
4. Remove the bolt from the thermostat housing.
5. Lift the thermostat housing off the engine.
6. Remove the old thermostat from the housing.
7. Inspect the thermostat for damage, cracks or other irregularities.
8. Replace the old thermostat with a new one.
9. Reinstall the thermostat housing and the bolt.
10. Close the hood of the vehicle.
