The heating system in your 1998 Buick Century pulls heat energy from the engine coolant and transfers it to the passenger area. You direct where that heat goes by adjusting the settings on the dash. The heater core is a small radiator that sits inside the vehicle cabin, and the settings on the dash open and close different vents to control the source of air (inside or outside) and where it goes (floor, windshield, dash). A fan behind the heater core determines how hard the air blows.
Lift the hood and prop it open. Makes sure the engine is cold. Disconnect the negative battery cable with a socket wrench or box wrench. Avoid using open-end wrenches on the battery terminals, as they tend to strip the bolt heads.
Place a drain pan under the radiator. Open the radiator cap. Open the radiator drain on the bottom of the radiator and the two coolant drains near the oil pan. You can reuse the coolant unless it appears cloudy and contaminated. Close all three drain openings once all the coolant has drained from the system.
Disconnect the inlet and outlet hoses of the heater core inside the engine compartment using a socket wrench. Be prepared to catch or wipe up any coolant that drips from these hoses. Drain the coolant from inside the heater core.
Unscrew and remove the lower instrument panel sound insulator from below the dashboard on the passenger side. Use a socket or screwdriver to loosen and remove the screws on the heater floor outlet. Remove the clips and take out the duct.
Loosen and remove the screws holding the heater core cover in place. Remove the cover.
Remove the retaining bolts holding the heater core in place. Remove the heater core.
Position the replacement heater core and secure the retaining bolts. Put the cover back on the heater core and reattach the screws and clips.
Reinstall the floor outlet duct with its screws and clips, followed by the lower instrument panel sound insulator.
Reconnect the inlet and outlet hoses to the heater core In the engine compartment.
Tighten all of the drains. Fill the radiator up to the base of the radiator neck with antifreeze, reusing the old coolant if it's clean. Fill the coolant overflow tank up to the "FILL" mark.
Reconnect the negative cable on the battery and start the engine, making sure you leave the radiator cap off. With the engine idling, look into the radiator and notice that the coolant level has dropped. Add coolant until the level is back up to the base of the radiator neck. Add coolant to the "FILL" mark on the overflow tank. Put the radiator cap on, making sure the arrow on it points to the overflow tank.
Squeeze the large return hose leading to the top of the radiator with the engine still running. The hose should begin to feel hot, indicating that the thermostat has opened and is functioning properly.
Check for leaks in the cooling system.
