Water flow restrictor to heater core (1970) - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 04-19-2019, 11:28 AM Thread Starter
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Water flow restrictor to heater core (1970)

I have replaced a heater core (leaking from a seam) in my '70 Mach 1 four times now. I've owned the car 25 years. Should there be a water flow restrictor going to the heater core to reduce the water pressure to the heater core? What does it look like and where does it go. Thanks in advance

70 Mach 1, 351C 4V , 4 spd , hood tach , Grabber Orange

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post #2 of 15 (permalink) Old 04-19-2019, 11:36 AM
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wowee that is a lot of work to do 4x

no water restrictions in Stock mach 1s

there is an vacuum valve in the inlet line only if you have AC but it just closes the water flow to the HC when the AC is on

what brand HC are you using. I used Modine back in 96 and thank god its still going.

I do a flush every 2-3 years about 1500 miles

you can try a water restrictor from a 91-93 GT. it will fit in the 5/8th hose and you can give that a shot.
cheap enough insurance anyways

or you can use a 5/8th brass petcock valve in the inlet line and just keep it half open.

1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
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post #3 of 15 (permalink) Old 04-19-2019, 12:26 PM
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Typically the water outlet on the engine feeding the heater IS a restrictor. What engine do you have?

Note the crushed inlet below. The hexagonal machined type has a very small, maybe 1/4" hole, drilled inside.

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Last edited by 22GT; 04-19-2019 at 12:29 PM.
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post #4 of 15 (permalink) Old 04-19-2019, 12:37 PM
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4 cores is a lot. If you figure one was factory and old- and maybe one was cheap repro- but still that leaves 2 more? any issue with battery going dead? Or using a trickle charger? (Wondering if maybe an electrical issue/electrolysis eating away at the core)

FWIW- I installed the brass shut off valve on mine- I generally don't drive in the winter BUT its a vert- so I do need a lil heat sometimes. If it was a FB- I would probably leave it shut off if I was in a warm climate
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post #5 of 15 (permalink) Old 04-19-2019, 01:10 PM
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Like 22GT mentioned, make sure your outlet is crimped. On the 64-66 Mustangs the outlet isn't crimped but I had some issues with the heater hoses leaking and a blown heater core so I just crimped it myself. It's been a year now, no heater leaks of any kind, and the heater still cooks me outta the car.

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post #6 of 15 (permalink) Old 04-19-2019, 01:30 PM
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In additional to previous comments already stated I can’t help but think there has been a change in quality in heater cores. I’ve got a 65/66 core from Ford parts back in the 60’s, brand new in the box. It is seriously heavy weight.... way more than the core available today.

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post #7 of 15 (permalink) Old 04-19-2019, 01:33 PM
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Its a closed system, the pressure will be the same. Flow thru the core will be reduced though. I would start looking to see if you can read for voltage in your coolant and see how much system pressure you are normally running.

1969 Mach 1 S code...2nd owner
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post #8 of 15 (permalink) Old 04-19-2019, 01:41 PM
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Replacing the radiator cap with a new 13 PSI one, or maybe even lower if your region isn't too hot, could solve the issue. The lower rated cap is a bandaid fix but just thought I'd throw it out there.

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post #9 of 15 (permalink) Old 04-19-2019, 01:49 PM Thread Starter
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No A/C. All of the replaced heaters have been Modine. Battery does not go dead 351C Yes what a pain replacing them!

70 Mach 1, 351C 4V , 4 spd , hood tach , Grabber Orange

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post #10 of 15 (permalink) Old 04-19-2019, 06:32 PM
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Have you had any of the cores checked out by a radiator shop? May give you a clue to move on to an answer.

1969 Mach 1 S code...2nd owner
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post #11 of 15 (permalink) Old 04-19-2019, 06:57 PM
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I had the same issue and went through several heater cores on my '69. The aftermarket water neck coming out of the intake did not restrict enough flow and would pop the core after a while (high flow pump, high RPM engine, and heavy PSI rad cap didn't help).

The solution was a 3/8" pipe plug with a hole drilled into it plumbed into the upper heater hose- this limited the pressure going into the heater core. The same core has been in there for several years now with no issues. I put a hose clamp around the hose where the resistor is just to make sure it stays put.
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post #12 of 15 (permalink) Old 04-19-2019, 09:27 PM
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Also pick up a heater control valve, like a 69-71 dodge or vintage air 46105-vuh from summit. It's an easy in line shut off for the heater core. Using the suggested restrictor above and this shut off will easily address your heater core prob. I ran both for several years.
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post #13 of 15 (permalink) Old 04-19-2019, 09:34 PM
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The Vintage Air Replacement Heater Valves 461171 might be a better choice... it's 12V electric so you can hide a toggle switch somewhere.

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post #14 of 15 (permalink) Old 04-19-2019, 10:16 PM
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Many Fords used a heater control valve.

https://www.dearbornclassics.com/hea...axie-1963.html

https://www.dearbornclassics.com/hea...1969-1970.html

https://www.autozone.com/cooling-hea...4_148104_13402


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post #15 of 15 (permalink) Old 04-20-2019, 10:20 AM
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On my '65 Galaxie with a 390 I had the same issues. What I found was that the length of the elbow in the intake is what made the difference for me. The original had a deep pipe extending past the threaded portion that sat maybe 1/4" off the floor of the intake manifold. When I switched to an Edelbrock alum intake and a new elbow, I kept blowing the lines off the heater core. You think yours was bad- mine requires removal of the fender!! I finally switched to an OE style steel elbow and it solved my problem completely.

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