The Buick Century made its debut in 1936. It was produced sporadically between 1936 and 2005 when the model was discontinued. The 1999 Buick Century was equipped with a 3.1-liter V-6 engine that produced up to 160 horsepower and 185 foot-pounds of torque. The thermostat on the 1999 Century opens and closes to control the flow of heat through the entire cooling system. A faulty thermostat can make it so that the car has no heat on a cold day and also can cause the cooling system to rupture if it sticks shut.
Raise the hood of the Century and position yourself on the driver's side, over the upper intake manifold area of the engine. The upper intake manifold is the large aluminum piece on the top of the engine; the air intake hose is connected to it. Locate the thermostat housing just in front of the intake entrance. A small black radiator hose leads to the thermostat housing and a hose clamp fastens the hose to the housing. Place a pair of needle nose vice grips or a radiator hose clamp onto the small radiator hose, as close to the thermostat housing as possible.
Place a drain pan directly beneath the portion of the engine you are working on. As you've clamped off the hose leading to the thermostat housing, you should experience very little loss of coolant. Coolant contains ethylene glycol, which is toxic to humans and animals; it has a sweet aroma and taste that attracts animals. Using a drain pan will ensure that you do not drip coolant on the ground.
Remove the thermostat housing cover bolts from the engine using a 3/8-inch drive ratchet and socket with a 6-inch extension. Turn the bolts counterclockwise until you can remove them from the engine by hand. Pull the thermostat housing cover off by hand. Set the cover and radiator hose to the side so you can access the thermostat.
Remove the thermostat in the center by gripping it with a pair of needle-nose pliers. Pull the thermostat straight up from the engine and discard it immediately into the drain pan.
Scrape any residual gasket material from the old thermostat off of the engine, using a razor blade or box cutter blade. Scrape away from the thermostat opening, so you don't drop gasket material into your cooling system. Visually inspect the thermostat housing cover as well to ensure that there is no sealant or gasket material on the mounting surface of the housing cover.
Install the new thermostat gasket to the bottom of the new thermostat. Install the new thermostat and gasket assembly into the thermostat mounting hole on the engine. Reinstall the thermostat housing cover by hand. Tighten the housing cover bolts to 80 inch-pounds of torque, using a 3/8-inch drive certified torque wrench and socket with a 6-inch extension.
Open the radiator cap and remove it from the radiator. Start the vehicle and place the heater control panel on full fan speed and the selector switch on defrost. This will heat the engine quicker and allow pressure to build up in the system. Place your drain pan directly under the radiator and the radiator fill hole, as fluid will come out during this procedure. Allow the car to run for approximately 15 to 20 minutes to force all of the air out of the cooling system. Shut the car off and add coolant to fill the radiator completely.
