Not long ago, I purchased a much needed new heater core for my S4. This was the first time that I’ve had to replace a heater core in an FC, so naturally I did a little digging in order to see how I might remove the heater core from the heater box, etc. Knowing that the heater box lives behind the center stack, I was aware that I would have to remove the dash before I had even begun to search. In reading over some threads that I found, it immediately became apparent that the general belief was that removing the dash was the only way to replace the heater core.

However…

I did stumble upon a few comments that dash removal was unnecessary — that, allegedly, there was an access panel underneath the dash that allows removal of the core with the dash in the car. “No!” claimed the nay-sayers, upholding the belief that dash removal was the only way to go.
One member went so far as to say that even if it was possible to remove and replace the heater core with the dash in the car, laying on your back wedged underneath the dashboard was not an appealing prospect.
I did a bit more digging around, attempting to find more evidence that others had indeed replaced their heater cores without pulling the dash from the car. Unsuccessful in my efforts, I was beginning to believe that those who had claimed to have performed the repair without spending the time to remove the dashboard were either liars or cheats (in some way…?).

Removing the dash really is not that hard, especially if you have done it a few times before. For beginners, the process is reasonably well covered if the effort is put into searching for those answers. I’ve done it several times in the variety of FC’s that I have owned over the years. Sure, there are the odd number of things that snap or are damaged during the process, especially when the weather has been on the cold side.. but it’s not a particularly complicated job.
In my recent case, the reluctance to remove the dash was to try and maintain my (relatively) rattle free cabin, and avoid some brittle piece of Mazda history shattering into a million pieces because of the low temperatures we’ve been experiencing (Hence the desire to replace an old heater core with a brand new one)

I’m here to tell the world, with absolute certainty, that replacement of the heater core is possible with the dash in the car. There are, however, a few minor details that are important to factor into your planning…

- The driver’s seat must be removed. This gives you room to lay down on your back to more comfortably work.

- The center console/armrest must be removed.

- The steering column must be dropped. This is very easy, and only requires that you remove the column trim, crotch, and foot vents. Note that you should leave one of the bolts for the column-to-dash bracket piloted, because you’ll be lowering the steering wheel onto your stomach when you remove and reinstall the core.

- The carpet *should* be removed, ideally… It is assumed here that your core is leaking in some fashion and has soaked your carpet, so removal will be necessary to clean the mess it makes. Also, you would not want to spill coolant onto your carpet when you disconnect the coupler hoses when you remove the old core. If you’re removing the carpet, then the passenger seat must also be removed.

To break it down into steps for you, this is the intended work flow…

- Drain off some of the coolant into an appropriate container.
- Remove both seats.
- Remove door opening sill covers.
- Remove finishing trim on both sides of the center stack.
- Remove kick plates from both outer footwells.
- Remove seatbelt buckles.
- Remove seat belt anchor from floor.
- Remove center console/armrest.
- Remove crotch vent and floor vent.
- Remove the steering column surround trim, and remove three of the four fasteners, leaving one bolt piloted to hold the column up. Disconnecting the electrical connections wouldn’t be a bad idea.

You should be able to remove the carpet from the car. This is a bulky, tedious process… so be careful!

Lay down a throw-away blanket where the carpet used to live, and get underneath the driver’s side dash. With a flashlight, you will definitely see the beige plastic heater box. You’ll also notice two phillips head screws holding the service cover on. Remove them and the cover, and all will be revealed.

Loosen the coupler clamps and slide the hoses away from the joint. Once this is done, the core simply slides out of the box and the new one can go in.
A top tip…. after you loosen the hose clamps for the coupler hoses, take a wee bit of dish soap on your fingers and lube up the metal pipes. This way you will be able to slide the couplers away from the joint to allow removal. It’s all a very tight fit, so be mindful of what you’re doing.

I’m including a few pictures of the cover itself, just for the sake of proof. ;-)
Don't mind the mess of wires.. I had pulled my stereo and gauge panel out of the center stack and was rearranging things.









As you can see, I had a few problems... An old muddied up core and completely deteriorated coupler hoses, which I had to replace.

A word on heater cores themselves… over time, they can get an internal build-up of crud, which insulates the core from radiating heat. This results in diminished heating capacity in the car. In addition to this, the fins of the core can become rather clogged up with dust a debris, again reducing your level of heat. So, if you’re sure of your coolant temperature, and you’re certain that the heater valve is functioning properly and the mix doors are operating, but you still have mediocre heat.. your heater core is almost guaranteed to be the problem. It’s simply the age of these vehicles beginning to catch up with them in more interesting ways.

 

I applaud your creativity and persistence but have to ask...
Having already done it your way, do you think it's easier than removing the dash?

 

Clokker, I think that if the dash was out of the car for some other reason, that it would be easiest to replace the core at that time. Obviously having the dash out is the ideal situation.

But... I believe if you're just doing the core itself, then you're probably best off doing it with the dash in place. I'm a pretty big man and wasnt too uncomfortable in the end. The worst part about the whole process was getting the core's pipes lined up. I bought a core through autozone and the pipes were not bent right, so I had to carefully move them to where they needed to go.

I'd definitely recommend to someone that they do this with the dash in. Wasn't bad.

 

Did you remove the carpet? I doesn't look like it. I would be inclined to go at with as little removal of stuff as possible. But then again, I'm of relatively slight build.

 

I did remove my carpet. As you can see, there was a bit of a leak and it soaked into the foam backing because it ran down the trans tunnel and underneath the carpet pad. I took those pictures after I'd started the process of removing the carpet from the car.

You could do this with the carpet in place, but it would require an old sheet to stuff underneath the heater box to protect the carpet in the footwell, and some old towels to increase the absorption factor. If you didn't care about your carpet, this is an option. Even if you do get a tiny bit onto the carpet itself, it won't soak through the plastic carpet pad, so extraction is totally possible.

 

irony, you supposed to remove the dash to remove the carpet... anyways you can cut here bend there. nice job i would do mine without pullingthe dash.

 

Good catch! I did forget to mention (because I've long since forgot), if you've never removed your carpet with the dash installed, you'll have to cut on either side of the heater box. I *think* that's it for cutting. Be careful to cut in such a way that you'd never know it...

I remember I pulled my carpet a few years ago so that I could soak it in dawn and degreaser and then scrub and pressure wash it. Came out really well.