here is the procedure as outlined in the service manual.
The heater core heats the air before it enters the vehicle. Engine coolant is circulated through the core to heat the outside air passing over the fins of the core. The core is functional at all times (no water shut-off valve is used) and may be used to temper conditioned air in the A/C mode, as well as the heat or vent mode.
Disconnect the negative battery cable.
Remove the cosmetic/acoustic engine cover, as equipped.
Remove the air cleaner and duct assembly.
Drain the engine coolant into a suitable container.
On the 3.4L (VIN X) engine, remove the throttle body and the throttle body tube to which it mounts.
Heater hose arrangement-3.1L engine shown, others similar
Heater hose arrangement-3.8L engine
On some 3.1L engine, a Quick-Connect fitting as used, which requires a special tool to separate the fitting
Opening the heater core case for heater core removal
Disconnect both heater hoses from the heater core. On some vehicles, accessing the firewall side heater hoses can be a challenge due to limited working space. In addition, some vehicles equipped with the 3.1L engine may have quick-connect fittings on the hose, requiring special tool J 38723 Heater Line Quick Connect Separator, or equivalent.
Remove the lower center console, if equipped. Additional information may be found in the Control Panel service instructions, found in this section.
Remove both left and right underdash sound insulator panels.
Disconnect the lower heater duct.
Remove the heater core cover. The sealer usually should be discarded and replaced with new sealer. Evaluate the condition of the existing sealer and the availability of new sealer.
Locate and remove the heater core mounting clip and bracket and remove the heater core from the vehicle. Use care as it will likely have coolant inside and could drip onto the rugs or seats.
Installation is the reverse of the removal process. After refilling the cooling system, bleed out the air and check for leaks as outlined in Section 1 of this manual.
Connect the negative battery cable.
If equipped with a 3.1L engine, remove the air cleaner and duct assembly.
If equipped with a 3.8L engine, remove the fuel injector sight shield by performing the following procedures:
Clean the area around the oil filler cap/tube assembly location.
Rotate the oil filler cap/tube assembly counterclockwise from the valve cover.
Lift the fuel injector sight shield up at the front and slide it from the rear engine bracket.
Reinstall the oil filler cap/tube assembly in the valve cover.
Before draining the cooling system, allow the engine to cool to relieve the systems internal pressure and to avoid scalding coolant.
Drain the cooling system by performing the following procedure:
Raise and safely support the front of the vehicle.
Remove and clean the coolant recovery tank.
Place a 2 gallon pan under the radiator to catch the coolant.
At the bottom of the radiator, open the drain valve and drain the coolant to a level lower than the heater core.
Remove the radiator cap and open the air bleed screw (2-3 turns) located on top of the thermostat housing.
After sufficient coolant has been drained from the system, close the drain valve.
Engine coolant is a hazardous waste; it should be stored for reuse or submitted for recycling. NEVER dispose of it by dumping it into the environment.
Disconnect and plug the heater hoses at the heater core.
If equipped, remove the lower center console by removing or disconnecting the following:
Automatic transaxle shift handle
Upper console trim plate from the front floor console by unsnapping it
Electrical connectors from the upper console trim plate and remove the trim plate
CD storage compartment from the front floor console by unsnapping it
Raise the front floor console armrest and remove the compartment mat
Console-to-chassis bolts and screws
Electrical connectors from the console and remove the console from the vehicle
Remove the lower instrument panel lower compartment by removing or disconnecting the following:
Lower right instrument panel insulator
Compartment-to-panel bolts and screws, from under the instrument panel compartment
Instrument panel compartment door screws and the door
Instrument panel compartment screws and plastic clips; then slide the compartment from the instrument panel
Electrical connector from the compartment
Ashtray and bracket, if necessary
Lower heater duct
Heater core cover and discard the cover seals
Heater core mounting clip and bracket
View of the radiator drain valve-Century, Grand Prix, Intrigue, Lumina, Monte Carlo and Regal
View of the fuel injector sight shield-Century, Grand Prix, Intrigue, Lumina, Monte Carlo and Regal
Exploded view of the instrument panel-Century, Grand Prix, Intrigue, Lumina, Monte Carlo and Regal
View of the heater core-Century, Grand Prix, Intrigue, Lumina, Monte Carlo and Regal
Install and connect the following:
Heater core in the vehicle
New seals on the heater core cover
Heater core cover and torque the bolts to 13 inch lbs. (1.5 Nm)
Lower heater duct, if removed
Ashtray and bracket, if removed
Install the lower instrument panel lower by installing or connecting the following:
Electrical connector to the compartment
Slide the compartment into the instrument panel; then, secure it with screws and plastic clips
Instrument panel compartment door and screws
Compartment-to-panel bolts and screws, located under the instrument panel compartment
If equipped, install the lower center console install or connect the following:
Console in the vehicle and connect the electrical connectors
Console-to-chassis bolts and screws, tighten in sequence beginning at the front right and continue in a clockwise order to 106 inch lbs. (12 Nm)
Armrest compartment mat and lower the front floor console armrest
C/D storage compartment into the front floor console
Electrical connectors to the upper console trim plate and snap the trim plate onto the console
Automatic transaxle shift handle and the cigarette lighter
Heater hoses to the heater core and secure with the clamps
Refill the cooling system by performing the following procedure:
Close the radiator drain valve.
If the air bleed screws (located at the top of the thermostat housing) is closed, open it by turning it 2-3 turns.
Slowly add coolant until it reaches the radiator neck.
Wait for 2 minutes and recheck the coolant level; then, add more coolant if necessary.
Fill the coolant reservoir to the COLD mark.
Close the air bleed screw.
Do not over-tighten the air bleed screw for it is made of brass.
Install the radiator cap and make sure that the arrows align with the overflow tube.
If equipped with a 3.8L engine, install the fuel injector sight shield by performing the following procedures:
Remove the oil filler cap/tube assembly from the valve cover.
Slide the fuel injector sight shield into the rear engine bracket and lower it into place.
Reinstall the oil filler cap/tube assembly in the valve cover. Twist it clockwise to lock the detent on the tube into the notch in the valve cover.
If equipped with a 3.1L engine, install the air cleaner and duct assembly.