The heater core in your 1997 Ford F-150 is a radiator-style unit used to heat the interior of your truck. Coolant flows from the lower radiator hose to and through the heater core. This fluid heats the unit, and a blower fan forces warm air through the core and into the cabin when the heater is turned on. A faulty or clogged heater core will leak coolant onto the inside floorboard on the front passenger's side. Replacing the heater core can be a complicated and time-consuming repair because of its location behind the passenger's side dashboard.
Raise the hood and disconnect both battery cables using a crescent wrench. Slide the recycling container underneath the radiator drain plug.
Remove the radiator fill cap. Loosen the radiator drain plug using a socket wrench to drain the radiator coolant. Once drained, replace the plug and tighten. Keep the recycling container in place to capture the excess coolant in the lower radiator hose.
Disconnect the lower radiator hose where it attaches at the radiator by loosening the squeeze-type hose clamp. Allow the excess fluid to drain into the recycling container.
Locate the heater core intake and return hose lines that protrude through the passenger's side firewall of the engine compartment. Disconnect the hoses from the core nipples by depressing the release clip with a flat-head screwdriver while turning the hose counterclockwise by hand.
Detach the Torx screws under the front dashboard that hold the dashboard soft cover in place. Reach under the dashboard and remove the mounting bolts attaching the dashboard frame to the interior firewall. This will allow the entire dashboard assembly to swing free and give you enough clearance to access the heater cover and core downward from the windshield.
Detach the interior heater core intake and return hoses from the core nipples by releasing the squeeze clamps using channel-lock pliers. Remove the hoses by twisting as you pull. Disconnect the heater core ground cable strap that attaches to the interior firewall with a single bolt.
Take out the four outer mounting bolts holding the heater core cover in place. Remove the four mounting bolts attaching the actual heater core to the interior firewall. Maneuver the old unit out and up toward the windshield. Be careful not to spill the coolant inside the heater core.
Install the replacement heater core in reverse, downward from the windshield and behind the dashboard. Re-mount the heater core, the core cover and the ground cable strap.
Reattach the intake and return hoses carefully to the core nipple on the firewall. The nipple hoses are different diameters to prevent you from incorrectly crossing the connection hoses.
Connect the dashboard frame and cover in reverse of the removal. Tighten all the mounting bolts. Be sure that the airbag remained connected during the repair. If it didn't, reconnect as necessary.
Reconnect the hoses located in the engine compartment at the firewall core nipple by snapping the hoses in place. Connect the lower radiator hose to the radiator and secure it in place using its squeeze-type hose clamp.
Refill the radiator with a 55/45 mixture of new anti-freeze and distilled water. Reconnect the battery and start the engine. Run the engine for several minutes to flush out any trapped air within the cooling system.
Test the replacement heater core by turning the heater on and off continually, observing the change in temperature. Check for leaks at all hose connections.
