I went thru it... and back!
Rebuilding the Heater Core of my 69 Mustang

Disclaimer: This is how I replaced my heatercore on a 69 MUSTANG Convertible with no A/C and no modifications in the dashboard area. This may not be the proper way or the way FORD would do this or would have done it, recommend it or would have recommended it. Although this worked for me and seemed to be the easiest solution and I try my best to describe in detail what needs to be done, I do not guarantee that it will be the easiest solution for you or that it will work for you. There is no guarantee that you will not scratch anything, spoil fluid over your carpet, get scratches on body parts or lose your mind on this trip to hell ... and back! This is for a 69 or 70 MUSTANG only, there is no airbag or anything else behind the glove box that shouldn't be touched. Anyways - use on your own risk.

These are the most complete instructions to replace a 69 Mustang heatercore anywhere on the Internet

It all started with fog or smoke coming out of the dashboard somewhere. Somewhere - I didn't locate it, or didn't notice any weird smell. At least it wasn't this electrical smell when some cable is burning. It didn't smell like this often described defroster fluid fog that does make you puke. I guess it helped driving a convertible. Well, it didn't help that much to realize it earlier. But when I first realized it during one of the last top down cruise days in November in Chicago where I was sitting with T-shirt and shorts in the driver seat pretending it is still hot enough to drive with the top down and looking at my wife in the passenger seat with winter wear and the window up - yes this MAY look stupid for driver-by's but - hey it's a cool car and that's what convertibles are for. It didn't snow, so what!

Yes I seriously got a bit worried when I first saw the what I believe was smoke and for some reason it never smoked or fogged in Idle so it wasn't easy to localize it. But now things started to make sense. It made sense that the carpet - one of the black Mustang rugs with the running Mustang logo - that the previous owner put in the car - had this weird discolor in the upper center part. Now it made sense that the additional 12V outlets I put it last year to have some hidden power sources for the GPS system (I only put it up when I get lost, or need to get back home using the Interstate after getting lost on a Route 66 Trip) were wet.

Yes things definitely started to make sense when I discovered there is a radiator - or heater core - behind the glove box. Yes I learn more and more about Mustangs. I used to have a 77 Mustang II back in Germany but I used it as a daily driver since it was my only car (besides the crashed Ford Capri and the broken down Honda Prelude) and never got too deep into surgery, and restoration was limited to modding and making it look hot, such as adding additional antennas and stuff. I own a 69 Mustang now, and this car is mostly original, went thru a major restoration a few years back by the previous owner and this candyapple red car with dark red interior will stay candyapple red with the original AM/FM radio until the end of its days. I may change the interior some day to black or will modify the engine but when I buy replacement parts, I really try to get NOS or OEM parts before I go aftermarket. Things started to make sense and after further diagnosis with researches on the internet I was 99% sure. It was the heater core! The only thing I missed was this defroster smell. No I have no idea how that is supposed to smell.
There was not much about replacing heater cores in a 69 Mustang on the internet but the few posts and comments on replacing heater cores for this model year didn't make me too excited about doing the job. I remember some notes about replacing heater cores in 64-68 Mustangs and how they are a Piece of Cake, going thru it on a 69 Mustang is a PITA and 'you definitely don't want to do it. You may just by-pass the core unless you really need the heater'. Yes some of them simply bypass the heater core - yeah who needs a heater anyway, especially if it's a convertible and not a daily driver. But I knew too good, when I start putting the hoses together to disconnect the heater core as a temporary solution, this will be a temporary solution for the next 10 years. And here's where you guys come into play. If you always postponed and delayed your heater core replacement, you may want to get it started with these instructions. It isn't THAT bad, it's a PAIN IN THE ASS, it takes you a few hours or - a couple of days especially if you have other commitments such as moving the lawn, having a job or other important priorities. It is a PAIN IN THE ASS but it's doable and don't even think about asking the FORD garage guys in town if they can do the jiob. THEY CAN'T DO IT BETTER THAN YOU and doing it yourself will save you at least I would say 1000 bucks, you may want to invest in better things. And besides that. You have a Classic Car and you better get your fingers dirty from time to time. Isn't this part of what it's about driving a 40 years old Mustang?

Anyways.... I got a Classic Mustang and I have a 3 car garage and asking the FORD guys to fix it is pussy. Apart from that I asked them to replace one of my headlights right after I got my Stang and went there for an initial check up. 'While you are on it, can you just replace the headlight bulb'. I ended up with a $120 bill only for a new headlight that retails at 30 bucks and still have a photo that I took with my blackberry of 2 guys sitting in front of the car trying to get the lamp removed. No, having to spend 2 days or more for labor and ending up with scratches on the interior is not worth it. And I am not saying that FORD doesn't do quality service - not more or less than any other garage at least. They will still have to read thru old manuals to figure out how to get the heater core replaced, it's not just plug and play and getting some computer interface connected to that magically fixes it. You will get dirty!

It was a cold November evening in a Chicago suburb when I went thru the list of things I would need for a heater core replpacement. I still haven't checked if the source of the problem is really the heater core or just a leaking hose or something totally different, but I thought with around 50 bucks for a new core, the parts aren't that expensive if it needs to be replaced. I ended up with a 200$ bill at Mustangsunlimited.com (could be any other aftermarket parts distributer) and I planned to do it during one of the cosy winter evenings so I will be ready for the next cruising saison.

Here's the Shopping List:

69-70 Mustang Cougar Heater Seal kit- NEW (eBay.com Pony-Xpress Vintage Mustang) $ 10
Heater Hoses
Adhesive (will be added)

If you ever lived in Chicago you may know that Chicago Winters my be bitter cold with temps as low as -20F and far lower windchills. So this year wasn't any different and having no heated Garage doesn't make you want to spend more time than necessary in there. You definitely want to wait until the ice on the garage ceiling is gone.

The Chicago winter went by, so went January, February, March. April. May was the first month with somewhat stable 60+ F and seeing the first Classic Muscle on a Saturday Grocery Shopping trip made me jealous. How about this Radiator Anti-Leak Fluid? In one of the forums on the internet I read about that this Anti-Leak Fluid wouldn't work but the powder that's also available would be the solution that wouldn't only fix your radiator leaks, but also save the world I guess. To make a long story short. After putting in two of the powder tubes I realized that they may fix the world but wouldn't fix your heater core. I let the car runnnig in idle for 15 minutes, 30 minutes, went for a ride in the neighborhood and came back with fogged windshield. But I had fun on my 1 mile trip. I missed driving my car.

Before I start it the next time, I get this heater core fixed! The next weekend went by with lawn mowing (I have a 0.5 acre lawn and a push mower powered by arms and legs), the weekend after with getting new flowers and mulch (yes it's a suburban thing I guess). If it goes on like this I will never get it fixed. So I guess the mulch will have to wait. My SUV got evicted from using the Garage and I converted 2 spots into a service garage with enough space to walk around the car with both doors open. Well I got it in sideways.

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Don't postpone it for another day, just get it started and that's what I did NOW. I got my box with parts ready and my toolbox and started to dismantle the passenger side. For this job and for most of the jobs on a Classic Car, it is important to have some decent tools. I gave up on cheap tools after I killed to wrenches just trying to replace my sparks last year so a Craftsman Toolbox MADE IN USA is what you want, unless you have something better already. Additionally you want some

screwdriver, + and -, also a set of the short ones
WD40 Spray
Liquid Soap or Vaseline
lighter fluid
a big box of garage tissues
a oil change pan for the cooling fluid
computer antidust spray
Sandpaper (fine)
black garbage bags
duct tape (get one that really works, i still didn't find a good duct tape - seriously)
electric tape (not black) and a pen, to label the cable connections
a sharp knife (carpet knife)
Heater Core insulation
black adhesive for weather stripping
cooling fluid

May 3, 2009 - going thru hell...

Before you start remember to

- MARK the cables even if you believe you won't forget where you need to connect them
- Put the screws in small bags and mark them

There were different opinions about how to get started and what to get removed in oder to get the heater core replaced. Some people say, you need to remove the whole dashboard. Some say, you will have to removed the whole heater box, the box where the heater core radiator is in. Well there may be a few other opinions, but I did it my way, more due to the fact that I gave up on removing the dashboard after I found out that I won't get all the screws removed safely, especially the ones on top of the dashboard, next to the defrost vents.

Here's what needs to get removed in order to get the heater core removed, and nothing more. There may be bit of advantage having a convertible, but apart from hitting my head less often than doing it in a Sportsroof or Coupe (I hit my head more than once) there's really no advantage removing the core space wise. As I said I gave up on the dashboard, but I had to remove the following parts - before you do it, remember you will end up with a lot of different screws, so you definitely want to make note of the screws that you removed so you don't end up using the wrong screws for the assembling part later or even worse - end up with spare screws.

What you should do at this point is to remove the NEGATIVE cable on your battery, since we will remove a few cables.

Now you may want to get your passenger side floor layed out with a few layers of black garbage bags and use the duct tape to put it together so that no dirt or fluid will ruin your carpet. You also want to put some garage paper towels or old shirts on top of it so they can soak the fluid that WILL spill out of the heater core when you remove it.

Here's the list of things I removed then

- remove all dashboard screws so you can lift it a bit, there are many and as I said, I wasn't able to remove the 3 screws on top of my dashboard but removing all the others gives allows you to lift it to remove other parts
- removed the upper panel with the clock and disconnect 2 cables for clock and interior lamp. Don't forget to MARK the cables
- remove passenger side sill panel (in order to remove kick panel)
- remove the side panel that's connected to the dashboard
- remove kick panel passenger side
- remove glove box insert
- disconnect glove box string (the things that holds the open glove box door in place)
- remove glove box
- remove dashboard side panel next to the radio
- remove radio knobs and radio face plate, I believe I removed that just to make sure I don't scratch it
- disconnect and remove the interior lamp underneath the glove box

I have a OEM center console in my car but I didn't have to remove it, in case somebody wonders.

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This whole disassembling up to here was a matter of minutes. And I found an old speaker that was sitting with the magnetic part against the metal of that car. It wasn't connected but somebody obviously used it some time in the last 40 years. I won't put it back in.


So at this point I am pretty sure that the cause of the dashboard fog is a leaking heater core. The bottom of the heater box, that's the big black/grayish box you will see after removing the whole glove box parts, definitely is wet and has a nice white/greeinish patina of dry cooling fluid and rust mix.

Ok, let's stop here and get the cooling fluid out of the cooling system. I did not flush the cooler, but this may be the safest and cleanest thing, but you may still end up with cooling fluid in the heater core. Here's how I did it. Remove the air filter so you will have some space to work in the engine compartment. Cover the carburator to ensure you don't end up with fluid or dust in there! Get the flat oil change pan under your car. Open the radiator. Remove the 2 hoses to and from the heater core on the waterpump. these are the 2 tubes that go thru the firewall and connect to the heater core behind the firewall. There will be a lot of fluid coming out them. Direct them to the oil change pan under your car unless you want to have them end up on the car floor or everywhere over your engine.

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In order to only remove the heater core, we do NOT need to remove the heater box. So we don't need to remove the screws for the fan in the engine compartment. One of my attemps to get the core out was really at some point to get the whole box out but I learned the hard way that this isn't necessary, so I skip the part where I attempted to unscrew the filter from the firewall, since it's not necessary, unless you really want to remove the whole heater box.

Back on the bottom of the passenger side, let's get the heater box opened. On the left hand side you should see two connectors, the one pole small orange one goes thru the firewall to the fan, the other 3 pole one, is for the fan switch on the control panel. Disconnect both of them and MARK them and more important, don't forget where you put them when you try to get them out of the way. I made the mistake not to write down that I put the 3 pole connector in the fender opening when I tried to get it out of the way. Believe me you want to write that down.

Now it may get messy, we want to open the box. The box has two parts. The front part we want to remove and the rear part that's screwed to the firewall and we want to leave it there. Both parts are connected with up to 11 clamps all around the box, where the front and rear part connect. You should be able to remove them with a screwdriver just by going underneath one of the sides of the clamp. Make sure you don't damage the box, an aftermarket box is $250 and you will have to go thru the hassle of removing it completely and you also don't want to damage the clamps. Although some aftermarket distributors tell you, you want to get replacement clamps for the heaterbox, the one I ordered, and they were for this model, were definitelty too small. Try to clean the original ones and use them afterwards unless they are totally corroded.

After removing all the screws, unscrew the screw on the right hand side that holds the front part to the upper metal part of the dashboard. Now the front part of the box can be removed. It may be a bit tricky to get the front part out of there now, but it works. Try to work the part down to the floor and make sure you don't scratch too much or slice a cable with the sharp metal parts. It shoudl definitely have helped that we removed the interior light here.


What you now see is the heater core or what is left from the heater core. You may see pieces of an old insulation, and rust. Just wipe everything dry at this point we will clean up the box when we removed the heater core. In case you wonder what the rectangular metal part is that you may find at the bottom of the floor now (unless it's still in the front part of the box). It will hold the core in the box. So don't trash it.

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Just a sidenote and something you won't run into but I did, since I didn't have this documentation. I spent some long hours trying to get the heater core removed now, after removing the 2 hose clamps for the tubes that connect to the core, replacing the black trashbags a couple of times, attempting to remove the screws in the engine compartment to get the whole housing removed. The main problem at this point was that there was NO way to get the left hose off the heater core. There is simply not enough space between the heaterbox and the firewall to use enough power to pull it off.

Since it was late I finished for the day, looked at my scratches, took care of the mosquito bites and took a shower.

May 4 2009 - still in hell...

I only had a couple of hours after work to work on my car. I thought I had enough power to get the hose off today but it was impossible. I took a break and cleaned the heating box front part with hot water and soap and used lighter fluid for the white greenish stuff on there. Also I put some WD40 on the connectors. This one looks nice now. Also removed all insulation of the rectangular metal part and had a hard time getting an idea how it would fit into the box. The hose needs to get off now to have the slightest chance to drive my convertible this summer. I looked for a carpet knife to cut it off and tried to cut if off from the core connection. You want to be VERY VERY careful here and watch your fingers. There is not enough room to navigate the knife easily and belive me I went thru this when I was a kid, cutting your finger to your bone with a carpet knife may not hurt in the first place and you only wonder what happened when you see the blood being pumped out of this nasty wound. You will end up with at least 6 stitches in emergency room in order to safe your finger. So be careful. I got the hose cut off after 10 minutes and I believe this is the ONLY way to get the heater core out of the heater box, so you definitely want to replace at least this hose. Carefully remove the core and make sure you don't spill too much fluid. Although the core may have a leak, there's still enough fluid in there to ruin your carpet.

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I spent the rest of the time cleaning up the box, and removing some old insulation. Having a bottle of computer dust cleaner is pretty handy here. I also removed some surface rust on the metal parts of the box and the vent entry with fine sandpaper. This works pretty good. I also got some rust dissolver but since the instructions talk about washing off the dissolver afterwards I wasn't so kean about it. After removing the surface rust, I used some lighter fluid on a paper towel, to clean it of dust. Some WD40 for the vent door and the metal parts of the heater cables won't harm. Same for the vent in the kickpanel.

I won't be able to work on the car the following days - lawncare and other things... and since I don't just want to get the new core in, close the box and put everything together I need to wait for a weekend where I will have a bit more time. Although you don't see all this since everything is behind your glove box you definitely want to do some further cleanup in there and make sure everything is dry.

I definitely want to fix my audio cables. I relaized when somebody fixed it with electrical tape and every move of the cable causes some distortion. Also I will need to do a bit of more dust cleaning especially behind the center part under the dash.

May 23 2009 - ... and back

I really need to get my car running again. The temps are hitting the 80's and my Mustang is still sitting in the Garage. I spent a few hours in the evening cleaning up some parts and replacing some stuff that I wanted to get replaced that are not related to the heater core. Today is the day to get back from hell. this is the Memorial Day Weekend and I want to go for a ride at least. I also had to order some weatherstripping adhesive for the insulation.

So here's to get your car running again. Put some insulation behind the heater core - I am not too sure if there was one but the one page manual of the insulation package showed one there. You may want to refer to the manual of your insulation pack if you want to be sure. Fix the insulation with the weatherstripping adhesive on the rectangular metal part. I also put two stripes of insulation on the metal part of the vent flappers in the heaterbox. I can't be bothered with the triangular or the other insulation since I won't be able to get this fitted without removing the whole box. Now get the new core into the heaterbox rear part. If you got the correct core, it will fit in nicely. Use your finger to put some liquid soap (or spare some vaseline if you have) on the inside of the hose to have it sliding over the metal hose part of the core and screw the clamp tight fit. Since we cut the other hose, use a replacement hose for the other connection and screw the clamp tight fit. Make sure the hoses are fit all the way over the metal parts. Reconnect the hoses to the water pump connectors.

Now it's a good time to see if the heater leaks. Reconnect the battery. Refill cooling fluid and leave the car running for a few minutes and watch the heater core. The core will become very hot. So will the hoses.

CAUTION: A running car in the garage - even with Garage doors open - can cause carbon monoxid poisoning! You may want to move your car outside before you test for leaks.
CAUTION: Never open the radiator cooling unit when hot! Wait until the car is cold before you add more cooling fluid.

Yay - the car runs and the new heater core isn't leaking. I will see if it still fogs when I go for a test ride later on. If this is the case, well, replacing the heater core at least was a good experience. So let's finish assembling the heater box and the remaining passenger side parts.

Disconnect the NEGATIVE battery cable.

Put the rectangular metal part with the insulation facing the heater core into the front part of the heater box. Look forward for a bit tricky navigation of this frontpart of the heaterbox to get it connected to the rearpart. The only way to get it in is from the passenger side floor all the way up behind the metal parts that will hold the glovebox until it fits against the rear part. It's tricky and needs a bit of moving back, forth and sideways but it will work. Be careful not to scratch the interior or cut any cables.

Now get the screw on the right hand side connected to the underside of the dash. We now need the 11 (or so) clamps. Remember, you may want to use the old clamps if they are still good. Look forward for another minutes of fun. I was only able to get 4 or 5 of these clamps back on and only after moving them a bit open. I bet there are tools for this I don't have. With the limited space here I was more than happy to get a few back on.

Now connect the single pole orange cable from the blower back to the heater box and - here's when I learned that next time I am going to write down where I put or hide any cable that I disconnect, since it took me 30 minutes to realize that the 3 pole connector for the fan speed I put in the fender opening, you may want to look there - ok conenct the 3 pole cable to the heater core.

Reconnect your battery and see if the blower fan works.

The rest is a piece of cake. We need to get the radio face plate and the sidepanel fitted. The kickpanel and brushed sill plate. The gove box door and the glove box as well as the cord that helds th e open glove box door in place. In order to assemble the clock panel, connect the interior light and the clock connectors and get your dashboard screws back in.

How many screws do you have left?

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List of cables that need to be disconnected:

List of hoses that need to be disconnected:

List of parts that need to be dismantled

Created: May 24, 2009 by Jerry
Revised: March 20, 2010 by Jerry

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