How to Replace the Heater Core on a '94 S10 Blazer

Although it's a task that requires the removal and replacement of several components, a patient weekend mechanic or do-it-yourselfer can replace the heater core in a '94 S-10 Blazer. Provided you label all fasteners and parts, and lay them out in order, there is no reason you cannot perform this task and save yourself $300-$600 in so doing.

Things You'll Need

• New heater core
• Short-handled Phillips screwdriver
• Long-handled Phillips screwdriver
• Socket wrench (1/4" drive wrench with 8" extension)
• Socket wrench (3/8" drive wrench with 4" extension)
• Sockets (1/4", 1/2" and 9/32")
• Adjustable pliers (channel lock or slotted groove)
• Masking tape
• Sharpie marker or pen
• Bucket (3-gallon or larger)
• 5/8" heater hose (2 to 3 feet in length)
• Carpet or pocket knife
• Container of antifreeze/coolant
• Container of one-use plastic rivets
• Shop rags or paper towels

Instructions

1. Remove the dashboard fasteners and retaining clips, beginning with the defrost vent fasteners. Lay them on a piece of masking tape, then cover them with another piece of tape of the same length. Write something simple like "def. cover" on the top and secure them.

2. Remove the fasteners at the passenger side kick panels and secure in another location. Set the parts in order from left to right so you can immediately recognize each part and where it belongs during reassembly.

3. Remove all fasteners along the bottom of the dash and secure them to remind yourself to replace them with the new ones during reassembly. Plastic rivets are made for one use only, so these will break during removal, but you can obtain replacements at an auto parts store.

4. Remove the panel underneath the steering column and secure, then remove the parking brake cable by compressing the spring at the lead keeper-piece and sliding it clear of the fork.

5. Remove the four 3/8" head bolts along the bottom of dash at the corners, middle and steering column and secure. Remove the fasteners at the center console, unplug the wire connectors and remove the tray. Secure.

6. Remove the steering column nuts and secure. This will allow you to adjust the column down to allow clearance for the dash to come out. Pull the column down slowly.

7. Remove the six screws fastening the heater core. You will find three on the top and three on the bottom. Move the cover to allow clearance for the removal of the old heater core. You will need to tear some insulation at this point, but you can patch it during reassembly.

8. Remove the steel strap fasteners, and secure. Step outside the Blazer and raise the hood. Twist the hoses off from the heater core supply and return the lines, firmly but gently. It may be easier to cut the hoses, which should be replaced now that you have come this far in the process.

9. Remove the fastener and bracket stabilizing the two heater core lines and secure.

   Stuff a piece of shop rag or paper towel into the two heater core lines to prevent spillage of antifreeze/coolant inside the vehicle as you pull it through the firewall opening. Pull the old heater core out and discard it.

10. Insert the new heater core from inside the vehicle. Under the hood, replace the stabilizer bracket and fastener. Cut two new hose pieces, and work them onto the new heater core lines with a twisting motion, being careful not to bend the lines. Back in the vehicle, replace the heater core cover and six fasteners.

11. Plug in all wires from the left to the right of the dash. Replace the dash and fasteners from left to right, starting with the top side. Make sure all the fasteners are tight.

12. Pull the steering column back up and into place. Replace the steering column nuts, parking brake cable, panel underneath the steering column and the tray at the center console. Replace the four 3/8" head screws and all the fasteners along the bottom of the dash. Replace the broken plastic one-use plastic rivets with new ones.

Tips & Warnings

• Save all receipts in case you need to return parts/ tools/ supplies.

• When removing the old heater core, have a bucket handy to catch antifreeze/coolant that will spill out when you remove the hoses from the unit. Also get some shop towels/paper towels ready to wipe up the spillage.

Resources

• Heater Core Supplier
• Heater Core Supplier