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  1. #1
    FEP Super Member erratic50's Avatar
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    Default Heater core on 1986 GT Conv factory air car

    Well - I just experienced one that makes you go WTF.

    I have an early production 1986 GT hatchback factory air car and my son has a late production 86 ragtop with factory air

    To change the heater core in my car without dropping the heater box out all I've ever had to do is remove the heater hoses then loosen the dash up and reach behind and pop the 2 7mm screws out. I had to nip 1/4" by customizing the lid but I can lift the top cover and pull the heater core out no problem.

    Meanwhile on my son's car I had to pry the heater box as far down as possible just to get the sound deadener out and I doubt I'll ever get it back in! The lid will barely move upward at all!

    I finally forced the lid up as far as possible the folded the flange on it over then cut the heater box even with the lip the heater core rests on.

    My question - why was this SO much harder on the ragtop car?! Are their heater boxes mounted higher or have different lid, etc?

    Also - before anyone gives us there is any crap about cutting the box, it's a daily driver with working AC
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    Last edited by erratic50; 10-02-2017 at 07:40 AM.
    -- James

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  2. #2

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    My 86 Convert has not got the AC, but to replace the heater core, after removing the Glove Box, I cut the hanger bracket for the dash which was preventing the Heater Core from being totally removed and then bent a piece of tin plate to form a splice [tack welded to one side and self tap screw fixed to the other] to make good the Hanger once the Core was replaced.
    Had been through the process of totally removing the dash previously, and knew how much trouble that was, so the splice in the hanger was way easier. Don't have a current pic of the hanger spliced, only before.Name:  Heater core 86.jpg
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  3. #3
    FEP Super Member erratic50's Avatar
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    Default

    We removed the brace. Interestingly mine never had that brace in the first place.

    Yea, heater cores on these cars is one of my least favorite jobs. Unfortunately I'm on my 5th heater core in my car right now..... and that one is also blown.

    My only comments on this over the years are:
    - what cures it .....less water pressure ...will also cause other failures on your motor if it's turned up. My heater started blowing air about 30 degrees hotter when I went to underdrive pulleys and my heater core still blew (with a restrictor) so I definitely plan to go back to a sane pump rate using a Cobra water pump pulley on my car
    - In recent years I've learned that LMR sells flow restrictors that were OE for SSP cars and in the long run if installed properly work pretty well but do not cure it.
    - waiting until the thermostat is open before getting after it helps a lot and often prevents blown core problems more often than not

    the water lines on the core we removed pulled right out when trying to remove the hoses so definitely be careful with yours. The restrictor on the over the motor metal hose side of the heater core inlet may avoid breaking the heater core while trying to install a restrictor.

  4. #4
    FEP Super Member bwguardian's Avatar
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    When I went through my 85 vert back a half dozen years ago I also had to do the heater core. Don't remember the details...other than being a pain. I do remember having to loosen the dash up, remove the lines and such at the firewall, and changing out the core. I didn't have to cut and/or modify anything.
    HAD
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  5. #5
    FEP Power Member plumkrazy's Avatar
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    Default

    Having to replace mine one of these days. Been thinking of adding a valve that closes off and or bypass the core in the summer days. Lots of vehicles are using them to help reduce cabin temps in the summer. Still need to look into what would fit.
    1 of 3 1985 Silver Grand Prix Capr's
    My first New car and still own 1986 Capri

  6. #6
    FEP Super Member erratic50's Avatar
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    Seems to me lots of late 70's early 80's GM cars used a vacuum operated valve to accomplish that. They always ran a bypass pipe 100% of the time. The valve controlled if water was allowed into and out of the core. When they failed you had no heat but it sure beats blown heater cores. Cars that don't have the hard lines front to rear would be way easier to fit with such an apparatus probably.

  7. #7
    FEP Super Member erratic50's Avatar
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    Just looked one car vs the other. The heater core lines on the ragtop are nearly 3/4" closer to the pinch weld than they are on the hatchback. What a pain!

  8. #8
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    WOW that’s freak n crazy, mind busted 2 months ago, but it’s a non ac car, about a 20 minute job to replace

  9. #9
    FEP Super Member webestang's Avatar
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    I feel your pain. I've done it twice in my 85 and once in my 88. Both were AC cars..........

    Scotty
    1985 Fox Notch 4-banger Ranger tube header Eastwood Royal Blue
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    1999 Mustang Coupe V6 Auto Chrome Yellow -Daily Driver.
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  10. #10

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    I used a 94 heater core it's an aluminum type. It's 99.8% the same size. I feel they have a bit longer life to them. 2nd on the restrictor.

  11. #11
    FEP Super Member erratic50's Avatar
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    I think when I get a chance I'm going to braze in a cross-over and a valves into the metal lines that go across the top of the intake on the 86.

    That plus a restrictor should do the trick and hide quite nicely under the intake.

    Valve wise, the GM ones would be perfect. Make it so they are closed unless hooked into full vacuum -- it's cheap insurance.

    Let that one soak in for a second...... Heater core gets automatically isolated any time the car is at WOT for more than a few seconds!

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