For 1990-2009 cars

1. Install a new O-ring seal.
2. Install the thermostat into the thermostat housing.
3. Install the thermostat housing.
4. Apply sealant GM P/N United States 12346004, GM P/N Canada 10953480 to the thermostat housing bolts.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

5. Install the thermostat housing bolts.

Tighten
Tighten the thermostat housing bolts to 20 N·m (15 lb ft).

6. Install the new O-rings on the coolant pipe.
7. Apply coolant to the O-rings.
8. Install the coolant pipe into the thermostat housing.