Thread: Heater Core alert

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  1. #1 Heater Core alert 
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    Hi everybody and Happy Thanksgiving!

    This past week I installed a new heater core in my wife's 2004 Grand Prix.

    And while changing out a heater core on any car is not a fun or easy task, there are some unique characteristics about changing one on a 2004-2008 Grand Prix that I'd like to share with you.

    My hope is you will avoid some of the grief I experienced if/when you change a heater core on your car.

    First of all I want to point out that I was able to obtain some very useful information about this task right here on this web site. Before starting your task, conduct a search for heater core on this site and you will find useful printable instructions that came straight from GM.

    The heater core is nested in the center of the instrument panel. The heater core has two layers of panels (one is a cover the other an air plenum) in front of it that are held together with both 7/32 inch screws (which seemed to be an odd size on a newer car) and plastic rivets that you will have to separate with a chisel and small hammer. If you have an air hammer/chisel that is small enough to fit under the dash that would also work.

    It's soft plastic, but it breaking the rivtes is still a tedious job since you're in an uncomfortable working position. Once you get the first plastic panels removed you will discover an air duct that runs under the carpet towards the seats. You cannot remove the heater core plenum without this three-piece air duct coming off first.

    I noticed the instructions from GM did not require that the front seats be removed while the instructions in my Haynes manual did. I kept the seats in, but I discovered at this stage of the job why removing the front seats was recommended. In order to lift the duct out and away from the plenum, the seats have to be out to allow enough room to lift out the duct. Instead, I cut a slit along one side from opening of the duct down and this allowed me to pull the duct away from the plenum side to side. When I assembled the heater core, I simply re-installed the cut duct from the split side and sealed it up with duct tape. It will hold and nobody will see the repair. This save the work of removing the seats. You will still have to remove the console, but that job isn't as bad as it looks.

    After the two panels are removed, you will find dimples next to the holes where the rivtets once were. The instructions state that you need to drill the dimples with a 7/16 drill bit from the inside out. Then use small sheet metal screws to attach the panels back to the HVAC case once the new heater core is back in place.

    Last, but not least, is the most critical discovery I made during this repair. And that involves choosing the brand of heater core. If you don't use an OEM replacement, which most people hardly ever do because of cost, I strongly recommend buying a Spectra Premium brand heater core. I found mine at NAPA. The first heater core I tried to install was from O'Reilly's and the brand was Murray. The tubes for it would not fit through the holes on the firewall. I struggled and fought it until I finally discovered why after comparing the tubes on the defective factory core to the tubes on the Murray core.

    The lips on the end of the tubes of the Murray core were higher, more pronounced, than the lips of the factory core. They were so high that they hit the section of the HVAC case that runs along the holes on the passenger side of the firewall where the tubes must exit to connect to the heater hoses. I could not get the tubes of the Murray core exit the firewall holes. Thinking I could have been doing something wrong, I went ahead and tried to re-install the defective heater core and it went right back in. The Murray core fit like O.J.'s glove.

    I looked on the NAPA web site and then at the store I compared the tubes on the OEM heater core with those on the Spectra Premium core and they were exactly alike and the Spectra Premium heater core went right in without an issue.

    So if/when you have to do this dirty job, remember to compare the lips at the end of the tubes of your old core with those on your replacement and make sure they are alike. This will save you some grief when putting it all back together.

    Hope this is helpful.
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  3. #2 Re: Heater Core alert 
    SE Level Member Ruben A Del Bosque's Avatar
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    nice write up. I'm working on mine at the moment. I think I can post some pics that can help walk people through. I was going to try to drill out the rivets but I think i will try your chisel method.
    My name is Chobies and i approve this message.
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