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How to Remove or Replace a Heater Core in a 1992 GMC Jimmy

1.

Set the emergency brake and remove the negative battery cable.
Push your seats all the way back and lower the backs.
Empty the glove box and dash shelves.

2.

Remove the rear view mirror. See Resources for details.

3.

Remove the ash tray and radio. See Resources for details.

4.

Remove the glove box door by removing the two screws holding it in. Then wiggle out the rounded arm on the right side. Set the door aside.

5.

Slide out the tray that holds the ash tray.

6.

Using a pliers, squeeze the clip holding the light that is in the ash tray and pull it through and into the ash tray holder. Slide out the light and clip and set the ash tray holder aside.

7.

Remove the glove box access panel by removing the two screws in the back of the glove compartment.

8.

Remove the passenger kick panel by removing the 4 screws holding it in place. The bottom front screw may be hidden under the rug. Set the kick panel aside.

9.

Remove the 5 long screws in the top of the foot well trim holding the foot well trim to the bottom of the dash board.

10.

Remove the 2 short screws on the bottom of the foot well trim holding the foot well trim to the firewall.

11.

The foot well trim will drop and the foam will be filled with antifreeze. Use paper towels to soak the antifreeze out of the foam. Set the foot well trim aside.
Now you can see the heater core cover. It is the large black rounded cover up against the fire wall.

12.

At this point you can soak up the antifreeze in the rug or you can do it later. I did it now because I didn't want to be getting antifreeze all over the place while I worked. I lifted up the rug and used rags to absorb as much of the stuff as I could. I pushed rags into the top of the rug as well. I rolled the rug in rags and squeezed until I could get no more antifreeze out. And still there was more!
I covered the rug with rags and put the floor mat on top of the rags for the rest of this project.

13.

Remove the dash bolt on the right side which is screwed through a bracket connected to the right side of the truck.

14.

Remove the bolt to the left of the dash bolt holding a bracket in place with wires connected to it.

15.

Remove the bolt to the left of the bolt just removed, in the center of the dash. The bolt is holding a bracket.

16.

Put you hands under the dash in the passenger area and pull back and up. Then move the dash down a little bit to set it on bolt base that you removed the dash bolt from.

17.

Locate the heater core cover which you can't miss. It's the large black rounded cover. There are 6 hex head screws holding it in. Start by removing the 2 screws on the bottom of the cover. These are the easiest ones.

18.

Remove the screw on the bottom right of the heater core cover. A right angled screw driver with a hex head comes in handy here, but you can probably just use a straight screw driver here.

19.

Locate the top left screw on heater core cover.

20.

Remove the top left screw on the heater core cover by using a screw driver, with an extension, through the ash tray opening or radio opening.

21.

Remove top middle screw on heater core cover. This can be accomplished either with a straight screw driver through the glove compartment. The head of the screw may not be seated flat in the socket, so do not force it when removing it.

22.

Get your right angle screw driver with extenders as shown.

23.

Remove the top right screw on heater core cover using the screw driver with the right angle and the extenders.

24.

Locate the foam covered heater vent hose coming out of the top of the heater core cover behind the glove box. Carefully pull this hose off and notice that there is similar hose on the other side in the radio compartment. Carefully pull this second hose off as well.

25.

Wiggle and pull out the vent deflector that the two hoses were attached to. It has two tabs holding it in place, but it should easily come out. You should pull it through the glove compartment and set it aside.

26.

Locate and remove the vent deflector sitting on the hump in the center of the two seats. There are two screws to remove.

27.

Grab the heater core cover with your right hand through the glove compartment and with your left hand under the dash. Pull it toward the back of the truck first and then wiggle it to the right until you see foam with black tape covering it on the left side of the cover. This foam goes around the vent that leads to the duct on top of the hump. You have to cut it on the bottom as shown and cut it on the top as well. When I did this, I pulled so hard that the top foam and tape just broke. In retrospect, I should have cut it.

28.

With the tape and foam cut, you should be able to pull and wiggle the cover down and out.

29.

Now you need to drain the antifreeze. See Resources for details on how to drain the antifreeze cleanly so you can put it back in.

30.

Since I have never replaced my heater core hoses, I decided to replace them since I had to remove them anyway. See Resources for details on how to replace them. You can remove the heater core filled with antifreeze and cause a bigger mess in the car or you can follow the steps below to empty the heater core before you remove it.
Locate the heater core hoses under the hood. They are on the left side sticking out of the firewall just in back of the antifreeze reservoir.

31.

Follow the bottom, smaller hose (5/8 inch) back to the engine block. Unscrew the clamp, slide it up the pipe, and remove the pipe off the engine block.

32.

Pull the hose up and out so you can have good access to it. Clean it off a little bit and make a circle with your thumb and forefinger around the edge of the hose. Put you mouth on it and blow. The antifreeze in the heater core will be pushed out into the radiator. Keeping blowing until only air comes out. Antifreeze is poison, so don't get any in your mouth.

33.

Unscrew the clamps holding the hoses on the heater core. These are really tough to get off. You have to twist and pull until they loosen. If you are replacing the hoses, you can use a sharp utility knife and cut a slit in the hoses where they connect to the heater core to get the hoses off.

34.

Remove the bracket that is holding the heater core pipes in place.

35.

Back to the heater core inside the car. There are 2 brackets holding the heater core in place, one are each side. Remove the screws on the bottom of each bracket.

36.

Remove the screw holding the top left bracket in place. You can do this through the glove compartment.

37.

Wiggle, twist, and pull the heater core until you get it out. Now go take a coffee break before you start the process of putting in the new heater core. See resources for the details on how to install the new heater core.

Tips and Warnings

  • Do not put any radiator sealant in your radiator. This will not fix the problem and, if it does, it's only a temporary fix that will eventually clog up your radiator and other coolant components.
  • Organize your screws in small labeled bags or labeled containers so you remember which screws go where. Do not guess or you'll be using the wrong screws some place.
  • This is a complicated job and took me 7 hours to complete, while taking all these lovely pictures and documenting every step. It took 3.5 hours to remove the heater core and another 3.5 hours to put everything back together and test it.