HowTo: 2G Heater Core Replacement

[Blk02Xtreme]

Finally got around to swapping in a new heater core today for my 1996 Blazer 4x4. Whew, what a eff'in job! I'm very familiar with s-10 dash assembly from stereo installs, but this still took me 4.5 hours beginning to end (few breaks in there) It was all straight forward, just lots of little time consuming bits. I'm doing this all from memory, after the fact, so don't be surprised if what I say
is a 7mm is actually an 8mm or 7mm an 8mm. Sorry, no pictures. There are too many bolts scattered and limity visability to take useful shots, so not much to work with. Pictures or not, I can pretty much gurantee you this is the best 2G heater core replacement procedure on the net.

Many people drain coolant first.. Not me, I wanted to make sure I could get the dash apart and access the core before I went that far Although, if your core is 100% busted and leaking badly, you may do well to drain as much coolant as possible out prior to braking the seals on the core casing inside the truck. Mine wasn't 100% busted though, just rusted through starting dead center of the core and radiating outwards. Didn't have too much fluid to clean up, but each
situation will be different.

Also, the glove box does not need to be removed. If you un-bolt all the "glove box bolts" all that will come off is the trim panel, HVAC vent cover, and the lid and latch assembly. The actual glove box is molded to the shell and cannot be removed separately. You should, however, remove the relay access cover. This allows you another much needed window for when your removing the core case cover bolts.

I started with dash removal, up top then down under the dash, so that's how this is laid out...

- 2 small torx screws for each dash speaker vent and then 1 8mm bolt under each grill securing dash to skeleton.
- Defrost vent pops out with a flat head, carefully here. Then there are a total of 4, 8mm bolts securing shell to skeleton.

Next up, remove the center dash trim panel. This is the large, snap on, assembly that surrounds your head unit, has the headlight / interior light switches, Push-button 4WD switch (where applicable), and the center HVAC vents.

- 2 Phillips head screws mounted upside down, secures top of cluster trim (with clear window), to dash shell.
- Pry the shell away from dash, don't force anything as it will come off.
- If you have push-button 4WD, unhook this wire harness first.
- Pull it out some more, and disconnect all the headlight harnesses, hatch button harness, etc from the far left side.
- Put tilt in full down position
- Turn key to ACC position, place foot on brake, and put gear selector all the way down to the '1' position. This is necessary on automatics only, and must be done so the trim panel will clear the column. Keep foot on brake while it's in gear, that's a no-brainer but is important never the less. Once you have the panel off immediately put it back in park and remove the keys (unless you like the sound of the dummy buzzer)

Time to remove your head unit and HVAC panel. Doesn't help a whole hell of a lot, but I wanted them out of the way as I'm sure most will as well.

- 4 7mm Bolts securing radio
- 4 7mm Bolts securing HVAC controls

Now move under the dash to the bottom most, black, trim panels. The ones that block you from laying on the floor and looking up under the dash.

- Lots of long 7mm bolts w/ washers securing these panels. Remove all of them and then the panels. Nothing will be attached to them so no worries. Some are in odd places, so if a panel feels attached somewhere - it still is.
- Next remove driver side and passenger side kick panels. No need to remove any ECUs you may find attached to either kick panel. Just make sure they are laying in a safe and secure way.

Now remove the hard plastic panels further up, interior trim colored. Starting from the large driver side panel that has the emergency brake release handle attached. If your not familiar with removing the brake handle, I'm sure your scratching your head about that by now. I'll explain how to disconnect the cable, but first you have to drop the panel:

Starting at top of panel, right below steering column, remove the two torx bolts. Under the dash, along the outer rim, you'll have some scattered bolts. Most are 7mm I believe, and most do not have washers attached.Two bolts in particular, one driver side and other passenger side, are the bolts that securing the light bulb housings for the under dash lights. Once the single bolt is removed, the light will no longer be attached to the panel. Don't forget to secure it somewhere safe up there before pulling the dash out. On the driver side only there will be a 7mm that secures the panel to the driver side HVAC vent. Once that bolt is removed, the small vent will no longer be attached to the panel and can be pulled off it's hose and set aside. Just note how it's mounted for re-assembly later.
Once that panel is dropped, you still have a problem. The e-brake cable is still attached to the handle, hindering all efforts to get that panel out of there. To remove the cable:

Reach under the dash and follow the e-brake pedal to it's unpainted, metal bracket. In that area you will see the black e-brake cable and the assembly it operates when pulled. Keep looking at it and pull the brake handle so you can see what all moves and how it works. The cable terminates in the same manner as a bicycle brake cable. Black shielded cable with a metal wire inside, at the very end of the wire it goes through a narrow u-shaped bend and then a big metal nipple keeps the cable from pulling through. Manually push just the arm down (don't use the e-brake handle for this or it wont work) and remove the cable from the bracket. Remove the cable guide grommet and carefully pull the e-brake cable out, and the trim panel along with it. It will make more sense when your looking at it, but it's easy.

Now for the steering column:
2 15mm bolts securing steering column to upper dash, they go in upside down. you'll have to be laying on your back to see them. Remove and steering column will drop so dash will have room to come down. It goes without saying, but be careful when you lower the column, there are a lot of things attached to it. I moved my seat up and used it to hold the column up some what, then if I needed the dash lower I simply moved the seat back some. Keep undue stress off the
assembly from just hanging there.
Now there are 3 main bolts under the dash securing the shell to the skeleton. They are each 10mm, and the only 10mm bolts used under there. Find one each on far left and right side, near where the top of the kick panel would be, had you not just removed it. The driver side bolt is less obviously placed and harder to get to. I use a 10mm deep with 4" extension to get it. The is also one near the center, in the area of the ash tray (which hopefully you've removed by now). Take note on the left and right sides here, you'll see that there are 2 large metal nipples coming out from the side of the truck, and that there is a bracket attached to the shell that rests on said nipples. The brackets are open at the bottom to allow you to lift the dash off the nipples.

Once all the trim panels and shell to skeleton bolts are removed, and the steering column is dropped, you can now lift the dash off the above mentioned metal nipples. Do it one side at a time, I started with driver side because it had the seat to support it. There is no easy way to explain this. Just carefully push, pull, twist, turn, whatever you need to do to get the dash shell to
separate and pull out from the skeleton. The further out, the more room you'll have to remove the core case cover; easily said than done though.

Heater core case cover removal:
By far the biggest pain in the ass out of the whole job. On the upside, all bolts are the same identical 5.5mm deal so you don't have to pay much attention to where they are being removed from, just that:

5.5mm bolt = case cover, securing straps, and inlet/outlet bracket bolt.

Only way your getting to them is a 1/4 Drive ratchet, 5.5mm shallow socket, and a 3" or 4" - 1/4" extension. There is one clip with a cable attached, mid-way down the box on the right side. Remove the clip but leave the cable secured to it. The two hardest screws are, 1) Case cover bolt in upper left most corner (It is recessed and you will cuss at it), and 2) inlet/outlet pipe mounting bracket (upper left once mounted, where the inlet/outlet pipes exit through the fire
wall). There is also one hidden in the bottom left most corner. Have to push the small passenger vent out of the way, use 1/4" extension with a 5.5mm on the end and a few choice words.

Once all the cover bolts are removed, grip the cover and pull on it so it separates from the seals. If you have a badly leaking core, this is where you may get wet. Good idea to have some towels down before you crack it open. Try not to damage those seals when your removing the cover, unfortunately it's a flimsy foam surround and easy to damage. Again, no method to getting this cover off and from under the dash. On the far left side the cover has to clear the inlet / outlet pipes, and this is the hard part. You don't have much room between the cover and the shell, even when the dash is pulled out a good bit. You really just have to pull on it real hard and pull the dash out to it's limits at the same time. Having a friend here is practically required. Have him
/ her hold the dash up while you pull the cover off. Has to be removed from bottom, so pull it down in that direction. Have fun with this part, just take some relief in that it pops right back on with much less effort.

Once inside, you'll now see your most likely rotted out core. Give it a stern look and curse it to the maximum amount allowed by law for causing you all this trouble and grief.

Take a break from under the dash. Go find a bucket and drain the radiator from the passenger side drain cock. You'll see a rubber hose coming down inside the pass. side wheel well, that's the drain hose and the valve is close by. Once the drain valve is loosened, the coolant will drain right out of that hose for a clean job. Kill a beer or twelve will it's draining, close the valve now so you don't forget to later.

Now's the opportune time to remove the heater hoses. Opportune because you have not yet removed the bracket from inside yet. I had some issues with the one on the left, it's of larger diameter and it's kinda awkward to get the clamp depressed for removal. My hoses were not seized on badly though, tugged for a minute on each and the popped off. You may or may not be so lucky, some are on there good if it's corroded.

Back inside to remove the core:
- 2 Mounting straps, left and right and they run vertically. Remove top 5.5mm bolts from opening at top of dash, and the bottom 5.5mm bolts from under the dash. Friend is required here to hold the dash again.
- 1 5.5mm bolt upper left corner of box. This is the inlet/outlet bracket bolt. Kind of a pain. Use of short extension is required.

Heater core removal
Now you can pull the core out. Have a friend hold the dash up. Pull it out from top first so that the inlet / outlet pipes move out of the firewall grommet a good bit. Now get under the dash and pull it down and out, at an angle. Remove core from under dash, careful not to spill coolant all over. Towels should be coming in handy right about now.

Get some towels or rags and wipe out the inside of your core case. It's sure to have grime and coolant all over. Try to replace the foam cover gasket as good as possible, will have to do this again later so doesn't have to be perfect yet.

Grab the new core, which will hopefully last much longer than the POS you just removed, and prepare to install it. Have a friend hold the dash up and get under there. Put back in same path you removed it, mind all the hard plasticHVAC vacuum lines and other wires / relay. Careful not to bend the inlet / outlet pipes, and insert them in towards the firewall at an angle, push up and straighten out as it goes into place. Push the inlet / outlet pipes through the firewall grommet
from dash top, takes some pressure but they will go. Make this the first 5.5mm bolt you re-install, to secure the bracket to the case. Once secured, go back and reattach the heater hoses under the hood, and secure the clamps.

Back inside...

- Re-install vertical clamps, bottom bolts first and top ones second (worked easier for me in this case) They take a while to tighten fully so make sure the clamps are completely on there, they won't move laterally when they are.
- Once core is secure, re-align the foam seal one more time and prepare to re-install the case cover.
- Install case cover from below, again mind the HVAC lines and other wires. Guide it in on the left side first, as it installs under the remaining part of the case (will make sense when you see it) The line it up on other ends and start installing the remaining 5.5mm bolts. More colorful language to ensue.

Case cover is back on, take a much needed breather.....

From here it's important to make sure all lines and wires under the dash are not going to be in the way when you start securing the dash. Give everything a once over and prepare to lift the dash brackets back onto the metal nipples on leftand right sides. Friend is important here, it's good if you each handle one side, at the same time. Careful, careful, careful. It's possible to crimp HVAC hoses here, HVAC vacuum lines, wires, etc. Keep an eye on as many components as possible as you guide the dash back where it needs to be. I secured the top bolts first, the ones under the defrost vents and speaker grills, because they were most easily accessible and will hold the dash on from above while you re-install the other screws.

- Raise steering column, and re-install the 15mm bolts on Torque to spec, which I don't have handy. It's important these bolts are torqued back on though, it is your steering wheel after all - don't risk it.
- Re-install all three of the 10mm lower, shell to skeleton bolts.

Those are the main shell supports and need to be taken care of first and foremost. Now:

- Re-install HVAC panels and stereo, in that order as it's notched.
- Install center dash trim panel. Automatics need column shifter in '1' position again, be careful not to break the Hazard switch when you getting the cluster trim in.
- Before clipping the panel in, re-attach wiring harnesses for headlights, 4WD buttons, etc.
- Clip panel in place, re-install the 2 Phillips screws at cluster window trim.

For the rest - hard, trim colored panels and black under shields, re-install is reverse order of removal. Route the e-brake cable safely and re-secure it to it's bracket. Don't forget the floor lighting, one on each side. Also the driver leg vent HVAC duct that gets the 7mm bolt, make sure the duct lines up with the vent as well. Install the kick panels, defrost vent, and speaker grills, and your done inside the cab.

Fill up and top off your coolant with fresh Dexcool, or green stuff if you converted. Start it up and check around the heater hoses for any signs of leaking.



Hell of a job, but gratifying when your done. No more Dexcool air freshener when I turn my heater on. I also corrected a kink in one of the supply hoses and am getting better flow through the upper vents now as a result. I tried blowing a bit of air through the inlet pipe on my old core, just to see how clogged it was. Well, no air came out the other side whereas simply blowing into the new one expelled air through the outlet. This is after a flush and fill I just had done 30k miles ago. Hope the wrtite-up will be useful for someone. It's involved but not impossible, the skinnier your arms are here - the better.

Thanks to 'rlith' for some general information I got from his posts before I began. Also credit to the Syclone / Typhoon Archive for This 1G Heater Core Tech Article (Clickable Link Here) Some information was useful, even on the 2G.

[Blk02Xtreme]

Don't say I never contribute anything

[chevyguy2121]

Will this work on my 98 blazer 4x4

[dantheman]

Nope in 98 they changed these things for the worse. I am very expericed with cars, and know the dash of s10s/blazers. It took me almost 9 hours to change mine. The heater core is also about $175


Good luck,
Dan

[dropped99jimmy]

i got my heater core for 36 bucks

[dantheman]

But for what year:

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[SickSpeedMonte]

Looks like I have a fun day ahead of me one day soon. I get the same coolant smell when the heater is on (or the A/C with the temp control knob on anything but full cold)

Is there any way to verify that it is indeed the heater core before I invest the better part of a day on this? There was a coolant leak that dripped down the motor and onto the exhaust crossover pipe before. I was told by a shop that worked on the truck before I bought it, that they thought it was a freeze plug. I used some stop leak and that has all but stopped from what I can tell, but I still get the coolant smell from the HVAC vents. That's why I need to know that it is indeed the heater core.

If I take that black trim panel off under where the glove box is, will I be able to access anything to find out? Maybe a pressure test from under the hood would be the best diagnostic.

[black_blazer]

Awesome write up...

This NEEDS to be a sticky !!

[MI95Dime]

Thanks so much for posting this walk through. It was very easy to understand even though it is a pain to replace.

[crux131]

My take, since I just did my 96 today( and some of yesterday....lol ).

I followed the route described in the Haynes repair manual. It had a few diagrams and pictures and made everything sound easy as hell. Don't listen they are lying bastards!!!! I expected a few extra bolts, but they didn't list half the stuff I blindly fumbled around for. I actually unbolted the main harness connector from the dash subframe( passenger side, visible when dash is pulled slightly away from the windshield ). I think this may have actually been fairly easy, if the manual had troubled itself to mention the size of the socket needed to undo the bolt.

I had to remove the heater controls and the radio, but this allowed me to pull the dash far enough that I could rest it across the seats. This gave me plenty of room in the floorboard to move and work on the core.

I am assuming the OP did not actually remove the entire dash frame???? Maybe reading comprehension Ownz me tonight( I am quite tired right now ). Pulling the entire dash only really involved pulling a few more nuts and bolts than described, and gave me a lot of room to remove the covers over the core. I may have done exactly what he described, but do not remember seeing mention of the main harness bolt. I you disconnect this and a few other plugs, you can pretty much rest the entire dash in the drivers seat( if you leave the door open ), and access to all the heater core screws and bolts are pretty much in plain sight.

Nice write up originl Poster. If I had seen it, I may have attempted this job differently than the manual showed it.


BTW, I used the hell out of the following sockets and drivers:

T30 torx for the torx bolts on bottom of the dash.
7mm socket was a recurring size....upper dash, speaker grille...etc.
8mm
t15 to remove speaker grille screws.
10mm....bolts holding dash at pivot brackets.
phillips head screw driver.
Original poster mentioned a 5.5 mm I think. I did not have this, but I used either a 5/32" or 7/32"( I can not remember ).

I replaced my heater hoses also. If they make a special tool for the spring clamps, It may really be usefull. I kept finding the clamps hard to keep a grip on with regular pliars. I used a variety of straight and adjustable pliars and was probably more frustrated by the hose clamps than anything else.

[americasfuture2k]

i looked through the gm dealer service repair site on how to replace my heater core. i have a 98. with auto controls. that sh!t looks like a b!tch. so im not messing with it. my brother is a assistant service advisor (or some shit) for caddi, and all those guys have all the correct tools and know how for this. im gonna bite the bullet and have them do it. after looking at what all is involved, i dont want to mess with it. and i know i will mess something up that will keep my truck from running correctly. so ill just leave it to the pro's. ya know, the ones without certifications but are allowed to cover your warrenty work. those guys.

[americasfuture2k]

i just said screw dealing with it and sent it to a dealer. they did it good! only cost me 430 with my brothers service advisor/employee discount.

[NC4x4]

Well mine did take me a handful of hours, but boy was it worth keeping those couple hundred dollars in my pockets.

[americasfuture2k]

i just have money to throw away i guess. due to my circumstances and the situation i am in, it worked out way better this way.

[TKA]

Thank you for the very much for this information! Im fairly new to this board, I don't own one of these trucks but my gf does (so its my responsibility to fix as well as my own ride) In the span of 9 hours today i changed the heater core, the thermostat, and the water pump. I feel like i lost my virginity to her truck today.
I wanna say thank you for the flawless write-up, perfect 100%, theres a couple parts that are a little bit cloudy and confusin but that was for parts of the install and really im sure the designers from isuzu (yes I said it) would be confused if they had to perform the "heater core ritual".

Perfection man, better explanation then haynes or any other repair books, I was gonna do a bolt and screw count with pictures but to much goin on in the interior like you said, too dangerous for digital cameras. Mostly though I just wanted to fix the frickken thing, I was gettin sick of buyin a jug of coolant every 3-4 days so she wouldnt cook the motor (shoulda made sure she got a jimmy with the basic cluster, idiot lights instead of "confusing" to read gauges). Sorry to ramble on I just feel like i accomplished somethin great today, even my parts guy was askin if I wanted to order a rad and the complete hose kit, cause hey I replaced all the hard shit anyways . Nothin but no leaks, no mess, just heat perfection!