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  1. #1
    FEP Power Member richpet's Avatar
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    Default Dumb question probably about heater core hoses

    I searched and didn't find it.

    Stupid me forgot: Heater core has a 5/8 and a 3/4 pipe. Which goes to the intake and which to the water pump? I know the restrictor goes in the small one (inlet) and I *assume* that goes to the water pump?

    Tried looking on line and didn't find what I needed. Not always good at that...

    It's a factory non-AC car. You know, the ones that changing out the heater core is a comparable breeze...

    Sent from my Pixel 3 XL using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  2. #2

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    No, the restrictor goes in the one coming off the intake manifold. That's the pressure side of the HC.

  3. #3
    FEP Power Member richpet's Avatar
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    Got it, thanks. I couldn't remember which (intake or pump) sent pressured water to the core.
    The larger 3/4" pipe on the core then plumbs to the water pump. Intake manifold to 5/8" heater core inlet (on the left if looking at it from the front) gets the restrictor.


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    Last edited by richpet; 06-27-2020 at 11:49 AM.
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  4. #4

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    I Just stuck a nut in the hose with a clamp to hold it steady....cux that's what i had around

  5. #5
    FEP Power Member richpet's Avatar
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    Intake manifold to core inlet (3/4" at firewall) with restrictor, water pump to 5/8" outlet of core.

    Why did I always think the inlet was smaller than the outlet? No wonder these were known to go through heater cores

    Sent from my Pixel 3 XL using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  6. #6

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    For anyone that ever develops a leak in the heater core & wants to bypass it until replacement can be done or do it during summer months,& if your model uses a metal coolant pipe assembly (like present on 86-93 Foxbodys) or similar with the same ID pipes (3/4" 5/8") Napa sells a U shaped bypass hose which has the correct ID size for each of the two hose ends.This beats trying to rig something up,since each hose end is made to fit the pipes exactly.
    The part number is 10743.
    Napa's listing for the ID of each hose end is 19mm & 16mm, which is the same as 3/4" & 5/8".
    Attached Images Attached Images  

  7. #7
    FEP Super Member erratic50's Avatar
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    I've always had a theory that if you put the hoses on a heater core backwards it would hold up better. Essentially that's a lot of what a flow restriction does at the end of the day. Only then it is 3/8" inlet, 5/8" outlet..... not 5/8 inlet, 3/4 outlet like you'd get if you flip/flopped the lines.

    really stupid design. GM has used a valve under the hood that's ran by vacuum for years to keep the heater core out of the water flow path when the heater isn't on. One of the few things that was done better in that era.

    I've had a 90 degree elbow hooking the two hoses together on my 86 ever since the last time I popped a heater core on it. That makes like core #6 or 7. Damn they suck to change so I've been avoiding it for the past 5 years.

    The design is faulty for sure. My most recent heater core held up for less than a day after I swapped to a Typhoon intake and the motor saw a few 6150 full powershifts. Aggravating - I had an SSP flow restrictor in it at the time. Thought for sure I blew it up when the antifreeze went everywhere. A few months later the power steering return line did a similar thing -- again I thought for sure she was a gonner because one foot was on the gas pedal on floor and the other was on the clutch grabbing gear past redline when it let go.

    An underdrive crank pulley and a Cobra style waterpump pulley slows down the PS pump quite a bit and the waterpump some .... just to 1:1 .... but together it helps keep things from letting go so often.
    Last edited by erratic50; 07-08-2020 at 12:46 AM.

  8. #8

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    We accidently hooked up the heater core backwards one time on my Dad's 90 Mustang, and the heater barely blew warm at all.
    Matt
    1984 Thunderbird -- 1989 302 HO, GT40 heads w/ Trick Flow springs, E303 cam, Edelbrock Performer 289 intake, Edelbrock 600 4bbl, 85 Mustang dizzy, Jegs o/r h pipe, Dynomax mufflers, Mustang AOD & shifter, Mustang 8.8 w/ 3.73s, Mustang front & rear sway bars, KYB 87-88 TC struts & shocks, and Mustang 11" front brakes.

    1988 Mustang GT hatch -- Explorer intake, GT40 heads with Trick Flow spring kit, Crane 1.7 rrs, E303 cam, 70mm MAF, 70mm throttle body, o/r H pipe, Dynomax mufflers, Kirban Kwik shifter w/ Pro 5.0 Deluxe handle, clutch quadrant & firewall adjuster, and 3.27s
    (86 Mercury Cougar 5.0, 89 Lincoln Mark VII LSC 5 speed, 80 Mercury Zephyr 4 door) sold

  9. #9
    FEP Power Member richpet's Avatar
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    That is my one concern as the restrictor has a tiny hole. I have never used a restrictor before.

    Sent from my Pixel 3 XL using Tapatalk
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

    "Never underestimate the power of stupid people in large groups"

  10. #10
    FEP Super Member Blainer's Avatar
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    I noticed LMR kit with the restrictor too. They have a good YouTube video on it. I've never put one in either. It's so the heater core doesn't get over pressurized.

    Sent from my LG-H873 using Tapatalk
    -Currently Searching for "The One"

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