How to Change the Heater Core on a 1989 Ford F-150

Damage to your heater core happens most often from a blockage within the cooling system. Failing to properly flush and fill the coolant at regular intervals allows rust and sediment to build up within the cooling system. This can clog your heater core's tubes, and cause them to rupture or leak into the cabin of your truck. Common signs of damage to the heater core include a sugary smell in the interior of the truck. The temperature gauge may also display in a higher position than normal. Your F150's heater core mounts behind the glove box, on the right, within the plenum chamber. With a few tools, changing the heater core should take one hour or less to do yourself.

Tools Used: Coolant drain pan, White painter's tape, Flat-head screwdriver, Five large shop towels, Philips screwdriver, Socket-wrench set

Change Heater Core

Lift the hood on your F150 and remove the radiator cap. If you have driven the truck recently, let the truck sit for one hour before proceeding with this repair. Place your coolant drain pan underneath the radiator on the passenger side.

Loosen the radiator's drain cock by hand until you see a steady flow of coolant coming out, but don't completely remove the drain cock. Allow half of the coolant to drain into the coolant drain pan, then quickly re-tighten the drain cock securely. The drain cock is on the lower left side of your radiator, and the best way to tell how much coolant to drain is to peer down the filler hole on the radiator. Once you can visibly see that half the coolant has drained, close the drain cock. Do not discard the coolant because you can reuse it to refill the radiator.

Locate the two heater-core hoses on the top, left side of the firewall. Label both of the hoses clearly with white painter's tape, so you remember which one goes where. Remove the hoses one at a time by loosening their retaining-clip bolts with a flat-head screwdriver. The hoses pull straight off once you have loosened each retaining clip.

Open your passenger door and remove all of the contents from your glove box. Disconnect the small black cable on the left of the glove box. The cable is held in place by a push pin, and you can remove it by using your thumb to push the pin out. Now remove the glove box by pulling it toward you.

Remove all seven of the small bolts from the "black" plenum chamber cover on the right, with your socket wrench. Take the cover off and set it to the side of your work area, along with its bolts.

Line your entire floor area beneath the heater core with five large shop towels. Remove the heater core by pulling it toward you two inches, and then lower it down from beneath the dashboard. Do this slowly and carefully because your heater core still has coolant in it. Set the heater core on top of your coolant drain pan, and allow its coolant to fully drain into the pan.

Reverse the removal procedure exactly to install your new heater core. Refill your radiator with the coolant that you drained into the coolant pan.

Tips & Warnings

Radiator coolant contains ethylene glycol, and various animals are attracted to its smell. Try your best to not spill any coolant on the ground, because animals will ingest it and cause harm to themselves unknowingly. If you do spill coolant, immediately soak it up with a towel.

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