The heater core in your Firebird resembles the radiator but on a smaller scale. When your engine is running, the cooling system circulates hot coolant through the heater core which is used to heat the interior of the car. A defective or clogged heater core will restrict this action. Damage to the heater core happens most often due to sediment buildup, which causes clogging and is directly attributable to poor cooling system maintenance. The heater core in the 1986 Pontiac Firebird mounts under the dashboard on the passenger side. You can remove and install a new one right at home.
Tools Used: Coolant drain pan, Flat head screwdriver, Socket wrench set
Install Heater Core
Raise the hood on your Firebird and remove the radiator cap. Place a coolant drain pan underneath the radiator in line with the drain plug. Loosen the drain plug until the coolant starts to flow out of the radiator. Allow the coolant to drain completely before closing the drain plug.
Locate the two heater core hoses on the left side of the engine compartment. They sit right beside each other and connect at the firewall to the heater core's tubes. Loosen the hose clamp on both hoses with a flat head screwdriver and pull the clamps back on the hoses 5 to 8 inches.
Pull both of the hoses off the heater core tubes and lift them vertically to allow the remaining coolant in them to back-fill towards the engine.
Open the passenger door and move the entire seatback as far as it will go. Kneel down so that you can see the silencing trim beneath the dashboard. Remove the three bolts holding the trim in place with a socket wrench then take the trim off and set it on the driver's side floor area.
Locate the heater core's cover. Look for a black rectangular-shaped piece of trim under the dashboard. Remove the four bolts with a socket wrench that hold it in position then take the cover off. The heater core should be visible.
Remove the four bolts from the baffle/support plate covering the heater core with the socket wrench. Remove the heater core by pulling it towards you 3 inches then lower it down from beneath the dashboard.
Install the new heater core exactly as you removed the old one. Tighten all four of the baffle/support plate bolts with a socket wrench until snug. Reinstall the heater core's cover and tighten all of its bolts until snug as well.
Place the silencing trim back into its original mounting position and reinstall its three securing bolts. Tighten them with a socket wrench until they're snug.
Connect both of the heater core hoses by pushing each of them back down onto the heater core's tubes. Slide the hose clamps on both of the hoses back into their original positions and tighten the clamps with the flat head screwdriver. Do not over-tighten the clamps to avoid collapsing the heater core tubes. After they're hand-tight, tighten them both an extra 1/2 turn.
Refill the radiator with the coolant in the drain pan then put the radiator cap back on securely. Start the Firebird and allow it to idle until it reaches operating temperature then check the heater core hoses for leaks. Turn the heater on high for 15 minutes and check for leaks once more.
Tips & Warnings
If your new heater core does not come with the baffle/support plate, transfer the one from the old heater core onto the new heater core.
If you choose to refill the radiator with fresh coolant, dispose of the old coolant properly. Call a local repair shop to see if they recycle coolant or find out where your local recycling center is located and dispose of the coolant there. If you spill any coolant during the repair, quickly clean it up because small animals are attracted to its smell, and it is poisonous.
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