How to Replace the Heater Core in a Pontiac Grand Prixby Contributor; Updated November 07, 2017
Items you will need
Replacement heater core
Replacement core seals
How to Replace the Heater Core in a Pontiac Grand Prix. The heater core is located right behind the front compartment and dashboard of the Pontiac Grand Prix. Its exact location depends on the size of the car's engine. If you need to replace the core, you must also replace the seals around the core and its cover.
Remove the Old Core
Unplug the cable from the negative battery terminal. Drain the coolant from the cooling system (make sure you use a clean container for it, if the coolant can be reused).
Remove the air cleaner and duct assembly if the Grand Prix has a 3.1L engine. Remove the fuel injector sight shield if it has a 3.8L engine.
Disconnect the lower floor console and both instrument panel insulators. Take off the outlet cover and core cover, and then remove and discard the core seals and outer seal. Unscrew the line clamp screw, retaining clamp and pipe retainer clamp screw.
Detach the heater core from the lower core case. Extract and discard all the seals (upper, lower, center and side) from the case.
Install the New Core
Attach new heater core seals to the lower heater core case, and then seat the replacement core to the case.
Reattach the pipe retainer clamp screw, retaining clamp and heater core's line clamp screw. Put on a new outer seal and core seals before connecting the heater core cover.
Install both instrument panel insulators and the lower floor console. Replace the fuel injector sight shield or air cleaner and duct assembly--whichever one you removed.
Fill the cooling system. Use fresh coolant, if you're not certain you can reuse the old stuff. Reattach the battery's negative cable.
Start the Pontiac Grand Prix's engine and let it run to normal operating temperature. Check the car's climate control operation and make sure there aren't any leaks.