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This article is now being maintained on HowTune.com: Changing the Heater Core on a GMC Syclone

Ah, yes, the heater core. I'm all to familiar with it. I've gotten so fond of changing heater cores, I've earned the nickname among the F.A.S.T crew as "Heater Core Bitch". One day, after a fun little trip down the road, I found a spot of coolant on my passenger side floor. I realized immediately that my heater core had decided it's life was over, and was about to puke its contents all over the inside of my truck. As it is a common problem with our trucks. It seems we have so much torque, that on those special occasions (ie. boost launches) the motor rotates under the hood enough to stress the hoses going to the heater core. This can bend and irritate the solder joints on the core, causing it to ooze a warm, moist gym locker fluid all into your carpeting in your pristine cockpit.

So, as soon as you notice the stench or the dripping fluid, grab some towels, put them down to prevent the coolant from getting to your carpet, it stinks! To remove the smell, if you didn't catch it in time, then peel back the carpet, soak up all the coolant that you can get out of the carpet and padding, and douse with your choice of fabric de-stinkers. I used FaBreeze, and it seems to do the job well.

Step One: Drain the Radiator

1)- Put a pan under the front driver's side of the truck. Get a large one, the coolant splashes all over the place cause it drains out onto the frame rail instead of strait down.
2)- Unscrew the plastic wingnut/petcock on the bottom of the driver's side of the radiator. It's real easy to get to if you already have the fender wells out, but you can reach it from the top if you undo the nut on the airbox, and move it out of the way.
3)- When the system is fully drained, tighten up the petcock, and replace the airbox.

Radiator Drain


Step Two: Removing Heater Hoses

1)- Remove the coolant overflow tank on the passenger side of the engine bay (3 - 10mm bolts). This is not a necessary step, but it allows better access to the hoses your going to fight with in a minute.
2)- Use a large pair of pliers move the clamp bands that hold the heater hoses to the heater core a few inches down the hose.
3)- Using that pair of pliers, clamp down the ends of the heater core's copper pipes that are inside the hose. Bend the hell out of them, just squeeze, till they are obviously no longer round. (be careful with that formed hose, its not cheap to replace). This will make yanking the hose off about 100x easier.
4)- Pull the hoses off the heater core
5)- Remove the Heater core's tube support ( 1 - 7mm hex screw). Its the little piece of metal in the shape of a "W" that attempts to prevent heater core breakage.

Coolant Overflow TankRemoving heater hosesRemoving Heater Hoses


Step Three: Interior removal (on your back boy)

1)- Remove light bulb from passenger side footwell, or disengage by removing it's fuse. This light gets hot, and will burn your arm quite nicely (my second syclone related injury).
2)- Remove passenger side footwell trim panel (7 - 9/32 hex screws). Its that dark plastic piece just under the dash.
3)- Remove passenger side kick panel (4 - phillips head screws).
4)- Remove ECM (1 - 9/32 hex screw). Remove the screw, and carefully pull it out from under the dash. You'll need to unplug it from the harnesses, and place it somewhere safe.
5)- Remove Ash tray
6)- Remove Radio Trim panel (3 - phillips head screws) The cigarette lighter simply comes off by spreading the two plastic arms away from the shaft on the back side of the trim plate.
7)- Remove Radio.  (2 Hex bolts)  Remove the bolt on the far right and left brackets, then pull the stereo out, unhook the wire harnesses and antenna wire.
8)- Remove access panel in the rear of the glovebox (2 - phillips head screws)
9)- Remove bolt on passenger side of truck that holds onto the dash (1 - 10mm Hex bolt)
10)- Pull out on the bottom of the dash, moving it out, and down to hook it on the tab that it was screwed into. This is to aid in removing the Heater core cover that needs a little room to move.

dash minus trim panalskick panalradio radio minus trimremoving radioglove box panalglove box panal


Step 4: Removing the Heater Core cover

1)- Removing the screws (6 - 7mm hex screws)  Four are easy to get to from under the dash  (2 on bottom, 2 on right side).  The top screws are accesible through the radio opening, and one in the glove box opening.  These are the real pain of the group.  Have fun, don't loose the screws ;)
2)- Disconnect the Heater Vent Hoses that are connected to the top of the cover.
3)- Begin Yanking!  Pull on the heater core cover from the bottom right side.   (towards rear of the truck).  Then try to move the cover to the right to disengage it from the ducting on the left side.
4)- Cut the tape.  There is some sticky foam stripping in the joint between the rest of the ducting and the cover, Cut it at the bottom(under the dash), and at the top (from the radio cavity).
5)- Rotate the cover so the bottom goes toward the front of the truck, and the top, towards the rear.  This is to get it around the heater core that rests inside.   You'll have to pull the "T" shaped ducting (look through glove box) out of the top of the cover to get it out.  Be careful, its plastic.  It will come out, just be nice, and wiggle till you manage to get that SOB out.


2 right side screws2 botom screwstop left screwtop screwcuting taperemovaland, its out!


Step Five: Removing the Heater Core

1)- Remove the hold down straps ( 3 - 1/4" hex screws).  There are 2 metal straps holding the Heater Core in place, Remove the left one (both bottom and top screws).  The right one doesn't have to be removed completely (its almost impossible to do).  Just unscrew the bottom of the right strap, and bend it up.
2)- Now, remove the Heater Core.  Pull, and rotate until you can manage to get it out.  It's most likely full of coolant, so be careful here.  You could put the tube covers off your new heater core onto the old one to prevent spillage (if you're new one has them, that is).

Know your enemytie down clipsempty that POS


Step Six: Reinstallation

1)- Make sure your new heater core is the same.  I got mine from Advanced Auto for under 30 dollars.  GM wanted A LOT more.  Ivan got his from Trak Auto for about the same.  Adam and Brian of FAST got theirs from Pep Boys.
2)- Transfer the foam insulation to the new heater core
3)- Cover ends of the new heater core to prevent debit from entering it
4)- You may want to bend the tubes of the new Heater core to make it easier to install
5)- Everything above... in reverse


Thanks to Ivan, for his Instructions helped me do mine the first time.  This installation is based off the instructions on his web page