I just recently completed this job with good results (so far!) using some general guidance I found online, although there didn't seem to be anything specific to my year and engine (2001 Ford Ranger 2.3L XLT), so I figured I'd just give a quick overview of what I had to do (and didn't have to do) to complete the job. This was a time consuming job, but not all that difficult, and in the end I saved about $1000 in repair costs (quotes ranged from $900-$1300)

Symptoms: fog in cabin, strong coolant smell when heat or defroster on. Some coolant loss. Some small drips from floor heater vent. This all suggested a leaking heater core. I was able to bypass the core for a couple weeks until I had time to work on it.

The dash had to be removed, but not all the way taken out. Just unbolted and pulled back enough to reveal the heater box and remove the core. Steps to remove the dash included:
- 6 bolts. 1 on passenger side near door, 1 on passenger side above dash near windshield, 2 on driver side above dash near windshield, 2 on driver side near door.
- Few trim pieces had to be removed, including the piece on the top/front of dash (no screws, just pops off), kickplates on both driver and passenger side, some others
- remove glovebox and a few electrical connectors behind it.
- did NOT have to remove airbag. Be sure to disconnect battery before doing any work though.
- remove radio
- remove cupholder underneat radio
- unscrew parking brake release and hood latch release from bottom of dash
- take out pinch bolt on steering column so that steering wheel can be pulled away. Did not have to remove steering column
- did NOT have to disconnect any gauges

After the dash was loose, it could be worked away slowly. The next step was loosening the heater box from the firewall, which included:
- removing supply and return coolant hoses to the heater core.
- 1 nut accessible from inside the cabin
- 4 or 5 nuts accessible from the engine bay. 2 of these were "hidden" and could only be accessed after taking out the first 2. The studs these nuts are on also go through the blower box on the front of the firewall and hold it in place. For these, one nut is on the outside of the blower box, and one is "hidden" underneath it. Also, there is 1 nut that could only be accessed from under the car by jacking the car up and removing the passenger side wheel and inner fender well. This one was really tight to get to. All these nuts connect to bolts on the heater box that penetrate the fire wall and hold the heater box in.
- There is a small metal tab that is attached to the heater box and goes through the firewall. I think this just helps hold the box in position, but it needs to come back through the firewall when you pull the box back.
- remove the PCM (unit near the space right above where the heater core hoses go through the firewall). This can be removed from the engine bay. Also, you have to remove the heat shield and grounding strap from inside the cabin. This is necessary in order to pull the heater box out enough inside the cabin to access the top of the heater core.

After everything is loose, pull the dash back as far as you can, supporting the steering wheel with a couple blocks and a blanket on the drivers seat and the dash with a bucket on the floor of passenger side. Then pull the heater box back from the firewall inside the cabin, which can be tough, since you have to get the bolts through the firewall, and they can get stuck on the threads. After it is out enough, there are 3 or 4 small screws on the top of where the heater core is. After taking these out, you can remove the cap and see the top of the heater core, which should then be free to come out by angling it correctly and pulling up. After it's out, if your core is really leaking, you'll see a bunch of coolant pooled up at the bottom of the compartment. I had to get a couple rags and clean it all up.

After this, it is just installing everything back in the reverse order. After the new heater core was back in everything was together, we also took a hose and funnel and temporarily hooked it up to the heater core inlet to fill the core with coolant, just to minimize the air in the system when we fired it back up.

Hopefully this helps someone else who is trying to take on this job. Overall, it probably took us about 7 hours (with 2 people) to finish the job, probably would take much less than that if we had to do it again. I'll try to upload some pictures as well.

 

Dash and heater plenum box pulled back enough to access heater core (new one shown)


View from underneath truck through passenger fender well. In this picture you can see one stud that comes from the engine side and goes through the firewall and has a nut that holds it on inside the cabin. There is also a hole in the firewall down here where a stud comes FROM the heater plenum inside the cabin and penetrates the firewall and is held on by a nut on the engine side of the firewall. This one was tough to get to and to get a wrench on, but I could do it with an open-ended wrench, about a quarter turn at a time.


View of 2 bolt holes near driver side door. These are for two of the bolts that hold the dashboard on.


Radio out


View behind (dash is out) and underneath steering wheel, where pinch bolt needs to be removed to disconnect steering column to allow dash to come free.


From the engine side. Hole through the firewall is where the PCM goes. Had to remove the PCM and metal heat shield (heat shield comes out from inside the cabin) in order to pull the heater box back enough. In this picture you can also see the black blower box that had to be pulled back a bit, as well as the u-shaped hose that I used to "bypass" the heater core temporarily until I could work on it.


PCM re-installed, as well as new supply and return hoses from coolant valve to the new heater core. These are molded hoses and have some defined bends, so they need to be purchased. I don't think you can just use a regular length of hose here, since it would kink. They were about $10 each.

 

Excellent write up, thank you