Heater Core Replacement

Page Revised: 10 May 2019


Article by
Eric Dess

Special thanks to Lee, Pete, Will, Bob and all at the NATO board for some of the information below.

Probably the number one most-dreaded task that people fear on these cars is the eventual need to replace the heater core. You can almost bet that on one of the coldest days of the year, your core will die and leave you without heat. Well, we're here to dispel some rumors—this isn't really that bad of a job at all. If you've got an enclosed area in which to work, some basic tools, and a few hours, you can do this yourself very easily. The advantage is that you'll be saving hundreds of dollars doing this yourself vs. having a shop do it for you. An average heater core change is $300-500 at a shop. Now if we told you that it can be done yourself for about $70 US and a few hours of your time, wouldn't you rather do that and save the money? Alrighty then, read on.

Heater Core

The heater core is essentially a small radiator that is tucked inside a plastic box behind your dashboard. Its main job is to allow coolant to flow through once the thermostat has opened. This brings in heat, and then you can run your car's climate system and fan to warm up the interior. Now this means that you have coolant passing through the firewall and into that box. If you haven't noticed by now, the firewall is just a barrier between you and what goes on in the engine compartment. Antifreeze is the only liquid that's allowed (by U.S. federal law) to pass through the firewall and into the passenger cabin, since it's not flammable. By introducing coolant into the cabin there is potential for a real mess. So be warned now that this is a slimy job. Hey, you want to save money, right?

Symptoms Of Heater Core Failure
  • Your radiator is full of fluid, the thermostat works fine, but you still have no heat.
  • You find a puddle of antifreeze on the passenger side footwell inside the car.
  • You smell antifreeze when you run the heater or defroster.
  • You see puffs of smoke coming out of the defroster or vent ducts.
  • Your windshield fogs up during or after you run the heater/defroster.

A way to double check this is to get the car warm, and touch both small hoses that go from the engine block to the heater core. If one hose is cold or lukewarm and the other is hot, you've probably got yourself a dead core. You can always have your coolant system (and core) flushed and hope that it clears up the problem, but if it doesn't, it's core replacement time for sure.

Parts Acquisition

Now that you've determined that the heater core itself is bad, you have to get yourself a new one. Now we're big fans of aftermarket parts as much as the next guy, but no matter what kind of deal you can get at the parts store, it is well worth the money to buy an original Ford/Motorcraft heater core. It's definitely the best built core on the market, and will far outlast most aftermarket ones. We've had people report that their store-bought core lasted a winter or two, and that's it. Sure, it's going to be cheaper...but do you really want to do this same procedure again in a few years? Just get the Ford core and be done with it. By the way, this same core was used in lots of Fox cars, including the Mustang, so if you want to shop online at Mustang parts places, feel free. Now you must get the core to match what you have now. So if you have A/C (which almost all of you do), then you have to get the core meant for a car with A/C.

Ford OEM Part Numbers:
Heater Core (cars with A/C) — E9LY-18476-A; also under the Motorcraft number HC-5
Heater Core (cars without A/C) — D9BH-184769-A, D9BZ-18476-B, E25H-18476-AA, E2FZ-18476-A, E4FZ-18476-A, E4FZ-18476-C

Bill has passed along a tidbit of info about the new core: "When you buy the new heater core, have a brace soldered between the inlet and outlet pipes. This will help protect the heater core from engine vibration and 'I will rip this hose off if it's the last thing I do' mechanics!"

Similarly, Darren shared a photo of the bracing on his core, that he had a radiator shop solder in for him.

In addition to the new core, you might want to pick up the hoses that go from the core to the engine block. They're relatively inexpensive and if you've never changed them, now is definitely the time to do that. And when the guy at the parts store asks, "Do you want new clamps with those hoses?", tell him, "Sure man, knock yourself out." Now you officially have all your parts. Time to tear into some stuff.

UPDATE: So we happened upon a great video on YouTube that highlights the procedure below, for the most part. Feel free to view it first, as it reinforces much of the information below, and you'll get a great idea about what you'll be getting into.


Removal Of The Old Core

Yeah, this is the part where most people freak out. No matter what you've heard, you DO NOT have to remove the entire dash. The dash only needs to come out far enough to get access to the heater core box. But that comes later; you have to disconnect a few things first.

Engine Compartment

If you still have the original-style R-12 refrigerant in your a/c system you MUST get it recovered at an official facility that can do so. They'll can it for you to use later if you wish, or you can convert over to R-134a. DO NOT let refrigerant bleed into the atmosphere! Now if you have R-134a already in there, bleed the system dry. Or if your a/c doesn't work (which I'm betting is the case for most of you out there), do nothing. The trick is to do the heater core swap within a day or two so you don't get a lot of atmosphere (and therefore moisture) in the a/c lines. That will prematurely rot out the system with rust.

You first have to remove the a/c accumulator on the firewall from inside the engine compartment. Disconnect the a/c lines going into the firewall (to the evaporator core), then remove the bolts from the strap holding the canister and remove the canister. After it's off, remove the second set of large nuts underneath that strap. These are the nuts that physically hold the core box to the inside of the firewall. You'll also have to remove the rubber coolant lines going from the core to the block (you'll likely need to drain your cooling system to do that). If the core hoses are old and are giving you fits coming off the core, cut them off lengthwise with a utility knife and peel 'em off. Once you've done this much, your work outside the car is pretty much done for the time being.

Passenger Compartment

You should NOT have to remove the following:

  • Radio
  • Instrument cluster
  • Glove box (although it helps a little)
  • Heater ducts
  • Ash tray on non-console cars

You will have to remove this stuff though:

  • Under-dash insulation (driver and passenger side)
  • Kick panels (driver and passenger side)
  • Console (if equipped)
  • Floor shifter and bezel (if equipped)
  • Console bracket (see photo here)
  • System Sentry module, if equipped (see photo here)

One more thing before getting too deeply into the job here: the following photos and descriptions are intended for the majority of 1983-88 Cougars and Thunderbirds. They may or may not be exactly what's in your car. For example, if you have automatic temperature control (ATC) then you may have a different setup behind the dash than a non-ATC car. Therefore these pictures and descriptions obviously would be different than what may be in your car. If you feel that you have something to contribute that would help others, feel free to contact us.

1983-84 Cougar/Thunderbird

Because of the nature of this older dashboard setup, you will have to remove more fasteners than on a 1985-88 dash. But don't worry, we've got them all outlined here for you. Very special thanks to Darren for providing the photos and info below.

To remove the dashpad there are a total of 10 screws that need to be removed. There are 4 total, 2 down in each windshield heater vent, on the top as seen here.

1983-84 Thunderbird/Cougar Heater Core Installation 1983-84 Thunderbird/Cougar Heater Core Installation

Next, remove the 2 special screws, one on each side of the dashpad.

1983-84 Thunderbird/Cougar Heater Core Installation 1983-84 Thunderbird/Cougar Heater Core Installation

There are 4 screws that attach the dash pad to the dash trim panels, two on the driver side and two on the passenger side. This is the one on the driver side to the far left to give you and idea of what you are looking for. Remove all 4, and then you can lift the dashpad off the top of the dashboard.

1983-84 Thunderbird/Cougar Heater Core Installation

There are 5 Philips screws holding the top of the dashboard to the firewall: 2 by the left speaker, 1 in the center, and 2 by the right speaker. Remove those.

1983-84 Thunderbird/Cougar Heater Core Installation 1983-84 Thunderbird/Cougar Heater Core Installation 1983-84 Thunderbird/Cougar Heater Core Installation

Remove the kick panels and unbolt the two screws that hold the lower dash (passenger side shown, driver side typical).

1983-84 Thunderbird/Cougar Heater Core Installation

Additionally, there are two more support braces: one is in through the glove box at the back of the radio (see the 1985-88 directions below), and another is below the dash on the driver's side, as shown here. After these braces are unfastened, the dash should be free enough to come out from the firewall.

1983-84 Thunderbird/Cougar Heater Core Installation

It may help to tie a bungie strap to the dash and hook it around the headrest to keep it pulled away from the cowl.

1983-84 Thunderbird/Cougar Heater Core Installation

There are 3 machine screws and 4 nuts that hold the air box in the car. One machine screw is self tapping and is at the bottom of the air box in the passenger foot well as seen here.

1983-84 Thunderbird/Cougar Heater Core Installation

Then there are 2 machine screws that attach the air box to the firewall at the base of the windshield which are identical to the 1985-88 setup.

1983-84 Thunderbird/Cougar Heater Core Installation

The A/C accumulator/dryer is in the engine bay and it will need to be removed from the bracket that affixes it to the firewall. This bracket is on two studs that are part of the air box. Once you remove the A/C accumulator/dryer from the bracket there are two nuts that affix the bracket to the studs. Remove the nuts and remove the bracket.

1983-84 Thunderbird/Cougar Heater Core Installation

Now you will see two washered nuts that will need to be removed so that the air box can be removed. The A/C accumulator/dryer is already removed in this photo. Also note that the heater core hoses have been removed—if you haven't done so yet, be sure to remove them before going any further.

1983-84 Thunderbird/Cougar Heater Core Installation

You are now ready to remove the 5 machine screws that hold the heater core cover onto the air box. When you remove the cover it may take some gentile prying but be patient and pry at multiple locations. Once you get it off, you'll need to clean all of the old seal off the air box and the cover. Silicone works well; optionally, a new butyl rope seal will do a great job and is actually what was used at the factory. It's installed on the air box and the cover in these pictures.

1983-84 Thunderbird/Cougar Heater Core Installation

Here is the new core installed in the air box and the inlet and outlet are through the rubber/foam seal for the firewall.

1983-84 Thunderbird/Cougar Heater Core Installation

And with the cover installed.

1983-84 Thunderbird/Cougar Heater Core Installation

You're technically now finished with the heater core replacement. Reinstallation is the reverse of the above.

Jump To End of Article


1985-88 Cougar/Thunderbird

Now what if we told you that there are only 7 bolts and nuts holding your dash to the cowl? Trick is knowing where they are.

(Thanks to Frank for sharing the photos!)

A diagram showing some of the bolt locations.

1985-88 Thunderbird/Cougar Heater Core Diagram

Remove the speaker grilles from the dash, along with the cover in the center of the dash. You'll see one 7mm bolt under each cover; remove all of them. Left speaker grille bolt.

1985-88 Thunderbird/Cougar Heater Core Installation

Center cover bolt.

1985-88 Thunderbird/Cougar Heater Core Installation

Right speaker grille bolt. That's 3 out of 7. 1985-88 Thunderbird/Cougar Heater Core Installation

Remove the kick panels (below the dash, to each side) and remove the bolt on each side holding the dash to the car. Driver's side. 1985-88 Thunderbird/Cougar Heater Core Installation

Passenger's side. That's now 5 out of 7—not bad, eh? 1985-88 Thunderbird/Cougar Heater Core Installation

The last two* will be 10mm nuts; they're usually painted blue so they're pretty easy to spot. Drop or remove the glove box and inside toward the back of the radio, there is a big metal bar that bolts to the outside of the radio metal support. Remove the nut from it and shove the bar off the stud.

1985-88 Thunderbird/Cougar Heater Core Installation

*NOTE: Some car owners (especially of Turbo Coupes) have reported that they do not have this brace. If you don't see it right away, you probably don't have it—skip this step.

For #7 you'll have to remove all 4 bolts holding up the steering column. They should be 5/8", deep well. The column will simply drop to the seat or the floor; it should be okay to let it hang there if you're not going to be long, but support it if you can.

If your car has a column shifter, Dan writes, "Before dropping the steering column, be sure to remove the PRNDL cable from the steering column before removing the nuts holding the steering column to the bottom of the dash (the white cable that goes from the instrument cluster to the column.) It is visible once the lower column shroud is removed.  I noticed on my car, that if it is not removed, the column's weight will hang on it and it will most likely break if not disconnected.".

Under the instrument cluster and back under the dash, you'll see nut #7 which should also be painted blue. The stud is aimed towards the floor and the nut is parallel to the floor. Remove it completely (don't just loosen it), and you'll now be able to wiggle the whole dash free. You won't be able to fully remove the dash from the car, but you won't need to when changing the core. You just need enough space to get to the heater box. What you want to do is get the passenger side out as far as possible. Be very careful when doing this—these are old dashes and they can crack easily. Have someone hold it, or support it, before going any further.

1985-88 Thunderbird/Cougar Heater Core Installation

If you find that you cannot get the dash out very far, double check to make sure all of the bolts are out. If you're sure they are, you may need to disconnect some harnesses in the passenger side kick panel area, by the computer.

The core box is on the passenger side; it's black and plastic. There are two straps on the top holding it to the cowl, and in each strap is a bolt. Remove those two bolts. Way underneath the box is another bolt, down by the transmission tunnel along the carpeting. It's tricky to see but you'll find it.

Be very careful of the hot-cold selector cable! If you don't disconnect it before removing the heater box you can risk pinching or breaking it.

1985-88 Thunderbird/Cougar Heater Core Installation

Once those 3 bolts are out the box can be wiggled from the dash and dropped down. On the top of the box is 4 bolts that hold the cover on; remove all 4 and the lid, and underneath—voilá!—is the core.

NOTE: Some owners have reported that it's a little more difficult to get to the top of their box. This may be due to having the ATC system. You may end up reaching through the glove box hole, or from outside the car, to get to the bolts on top. Just be patient and you'll get them.

1985-88 Thunderbird/Cougar Heater Core Installation

NOTE 2: Another owner has reported that on ATC cars, you MUST remove the entire blower assembly from the car in order to reach the screws for the lid. He says: "The location of the bolts that encase the heater core itself are not conducive to being removed inside the car. They don't face the firewall. There are five 7mm bolts that face the top of the dashboard, and you will never have room/leverage to get them out inside the car, so the assembly MUST COME OUT. Once out, just remove the bolts, and put the new core in." 1985-88 Heater Core Installation

Now you may notice that there's another little friend hanging out in the heater box with the core. That's his buddy, the A/C evaporator core. Most people can simply ignore it. Now if you have removed the A/C system or are going to, then this is the perfect time to remove it, but be careful: you have to cut up the top of the box to get it out, and that ruins the top. It may be possible to find a factory non-A/C lid but we wouldn't put too much faith in finding one easily. Silicone is about the best way to repair that lid afterwards but that's okay, because you're going to need silicone anyway.


There's nothing tricky here—simply swap the old core for the new one. Now there is a weird rubbery/wire seal inside the lid of the core box that probably will fall apart when you removed the lid. It's technically a hermetic seal but it's shot after you've broken that seal. Take all of the old seal out and hit the lid with generous amounts of silicone before you put it back on. Also, if your core has been leaking into the passenger footwell, you've probably got yourself a miniature green ocean in the bottom of the box. Clean all that stuff out and get it nice and dry.

Once you're done, you're ready for reassembly, which is—no surprise—the reverse of all the above. Don't forget to put the coolant lines on under the hood, and bolt up the rest of the A/C stuff. Fill the cooling system back up, reconnect the battery, and start the car. Immediately turn on the heater, full blast. Let the car warm up until the thermostat opens. You should then feel a ton of heat inside the vehicle...if so, you've done your job properly and can now leave that extra jacket in the house. Open up a cold one to celebrate, 'cause you deserve it!

While You're In There...'s been suggested by Curt, a professional mechanic, that you may want to consider replacing your blower motor at this time, while the dash is apart. If your car has a lot of mileage, or you hear a grinding/squeaking noise every time you turn on the fan, chances are your blower motor is going bad on you. A new blower motor should run around $50 U.S.

Darren also suggested that now would be a great time to install the heater core flow restrictor in the inlet hose to keep the core from popping at higher RPMs. It can be found under the Ford Racing part number XR3Z-18599-AA.


All this probably sounds like a lot of work but it's really not. Ford tells their dealerships that they have 8 hours per car to do the change. You'll probably do it in 3-4 hours tops. The hard part is the a/c stuff; once you're past that it's a piece of cake.