The 1992 Chevrolet S-10 pickup shares a platform with the GMC Sonoma. The heater core is actually a small radiator mounted inside the cab on the passenger's side of the S-10. When the heater is turned on, hot coolant is circulated through the core. A fan blows air through the core where it is warmed and routed through the various vents.
Park the S-10 on a paved level surface. Set the parking brake. Allow the engine to cool down before working on it. Remove the negative battery cable with a ratchet and socket.
Remove the radiator cap. Make sure the engine is cool before you do this. Find the radiator drain plug at the lower passenger side of the radiator. Place a large drain pan under the drain plug. Unscrew the plug by hand, and drain the radiator into the drain pan.
Follow the heater hoses to the passenger side of the firewall. This is where the hoses hook to the heater core. Loosen the hose clamps with a flat screwdriver. Wrap some masking tape around the hoses and mark them so you can put them back on the right heater core fitting. Twist and pull off the hoses.
Remove the lower side panels from the dash by removing the two Phillips head screws.
Remove the two Phillips head screws from the instrument panel trim panel. The panel is mounted to the underside of the dash, directly above the instrument panel. It includes the right and left air vents and radio cover. Pull the panel straight back to disengage the clips that hold it to the dash. Remove the electrical connector from the back of the panel. Set the panel aside.
Use a ratchet and socket to remove the two small bolts that hold the radio to the dash. Slide out the radio and disconnect the electrical connector and antenna. Set the radio aside.
Use a ratchet and socket to remove the bolts from each end of the underside of the dash, then use ratchet and Torx bit to remove the two Torx screws at each end of the underside of the dash. Use a ratchet and socket to remove the four nuts that hold the steering column to the dash and firewall brace. Allow the steering column to hang down. Remove the center bolt from the underside of the dash.
Use a flat screwdriver to pry the speaker grills and defroster grills from the top of the dash and remove the small bolts that are now exposed. Pivot the entire dash downwards. Reach behind the dash and remove any other electrical connectors. Remove the bolt from the center of the main electrical connector on the driver's side of the dash and disconnect it. Remove the entire dash from the S-10.
Find the heater core cover on the passenger side of the S-10. There is a thick wire brace attached to the center of the cover. Use ratchet and socket to remove the bolt that attaches the brace to the center of the cover. Use the Phillips screwdriver to remove the six screws that hold on the cover. Remove the cover.
Use a ratchet and socket to remove the four mounting strap bolts that hold in the heater core. Remove the straps. There is a strap on the top and bottom of the core. Use the ratchet and socket to remove the small bolt from the clamp that holds the two metal tubes that run from the heater core out to the firewall. Pull the heater core straight back to remove it.
Reverse these steps to install the new core. Refill the engine with coolant, start the engine and check for leaks. If your coolant is still clean, you can reuse it.
