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Discussion Starter #1 (Edited)
A few years ago I happened to be in the right place at the right time in Arkansas running into a car show with loads of Mustangs to look at. Lots of ideas gathered for my restromod, one of which was from a 1965 with a late model ~1985 5.0 (302) installed. Of course, I was also looking for certain items that were on “the list” to work on next for my ride. One list item was to get the original heater working that was disconnected due to a leaking heater core. I also had the original supply rubber tubes “hanging out” and I always thought that they just looked silly running across the top of the engine. For my ride I like to stay as original as possible, upgrading to modern when newer function outperforms the original form so I made the jump to hard supply lines and an aluminum heater core with extended supply lines (keeping leaks confined to the engine bay). While I was at it a complete heater box rebuild was also performed, removing the paint, and clear coating to look similar to original. Here are the steps to accomplish the hard-line upgrade with some heater box pictures added.

First, pictured are the heater supply lines just above the valve cover on this original set up that I wanted to upgrade.
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The goal was to upgrade the hoses to hard-lines and upgrade the heater box. This required reworking the fuel supply line to make space for the hard lines and a decent amount of ‘trial and error’ to find the right rubber supply lines to connect the upgraded heater core with the late model hard lines.

Heater Box Rebuild
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  1. Aluminum Heater Core with Extended Tubes
    • P/N: C5DZ-18476-ET
    • Note: This heater core is an modification upgrade from original and has the extended tubes (pictured) that push the hose connections and hoses to the engine bay rather than under the dash (the original style) similar to more modern mustangs in order to relocate any potential leak to the engine bay instead of the interior carpet.
  2. 1965 1966 Mustang w-w/o AC; 1967-68 w/o AC Mustang Heater Seal Kit
    • P/N: C5ZZ-18500-A
  3. 3M Black Super Weatherstrip and Gasket Adhesive
    1. P/N: 08008
    2. Note: If you have the knack for attention to detail and following rules pay attention to the directions for this adhesive that explain how to apply to both parts, let dry, then press parts together to adhere.
  4. Scott Drake Heater Cable Clamp And Screw 1965-1968
    • P/N: 378897-S
  5. Lots of work to strip old black paint and repaint/clear coat this early model heater core that was in pretty good shape and had most of the parts in tact. Note that this model is pictured without the thermostat on the front that was added on later models (one of my reasons for keeping it rather than purchasing new).
Additional Heater Box Parts – I didn’t use/need these, instead reusing original parts, however listing here to save the search time.
  1. Scott Drake Heater Core End Cap 1964 1/2 - 1968
    • P/N: C5ZZ-18500-C
  2. Scott Drake Heater Box Components – Single Clip
    • P/N: C0DF-19A779-A
  3. Scott Drake Heater Housing Clip Set 1965-1973 (8 clips)
    • P/N: C0DF-19A779-A
  4. Scott Drake Heater Cable Set 1965-1966
    • P/N: C5ZZ-18518-52-K
Heater Box Restoration – These links provide most of the steps used to rebuild. For my rebuilt I fortified/rebuilt the clip locations with Grey JB Weld (rather than fiberglass mentioned in the videos) which worked great! Paint scheme is similar to original with some stainless hardware added.

Article
Video
Hard Line to Heater Core
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  1. 1986-93 Mustang Heater Tube Assembly w/o Coolant Tube 5.0/5.8
  2. Late Model 1986-93 Water pump to hard line supply tube
    • P/N: Motorcraft KH307
  3. Gates Molded Heater Hose Inlet 5/8" x 5/8"
    • P/N: Gates 18705
  4. Gates Molded Heater Hose Outlet 5/8" x 3/4"
    • P/N: Gates 19249
    • Note: This part took the most time to find and is the secret to success for this upgrade. The part is originally from a Volkswagen and was found after searching through all Gates hoses by size and picture, trying the closest matches until success.
  5. (Optional) Gates Molded Heater Hose 5/8" x 3/4"
    • P/N: Gates 18743
    • Note: Use this “U” shaped tube to temporarily block off the heater core as needed during installation, especially if you still want to drive your car mid project prior to heater box completion.
The Great Divide – Matching the old to the new
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Note that I added original hose to the extended heater core tubes for insulation and to seal the firewall gap around the tubes.

The Money Shot
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Fuel Line Setup – Modified to fit along with new hard line.
Parts listed in part order from Edelbrock 14054 to Edelbrock 1725 fuel pump. Banjo fitting was also slightly bent inward in order to pass by hardline temperature sensor block off (Edelbrock 9127 – Black 3/8” NPT Pipe Plug) that was not used.
  1. Fuel Intake with Banjo fitting (comes with 8130 fuel filter)
    • P/N: Edelbrock 8134
  2. Flare Union -6 AN
    • P/N: Russell 660350
  3. Fuel Filter (purchased with 8134)
    • P/N: Edelbrock 8130
  4. Stainless Steel Braided Fuel Lines
    • P/N: Edelbrock 8124
  5. Adapter couple swivel Straight -6 AN
    • Russell 640000
Results:
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Additional Considerations:
Flow Restriction Insert
  • On some models a flow restriction insert is used (Mustang Heater Core Flow Restrictor P/N E7VY-18358) to reduce the water pressure in the core while also keeping the heat in the engine when cold. The hard lines have one ¾” fitting and one 5/8” fitting, so the restriction insert is not needed due to the inherent restriction provided by these tubes.
Hose Routing
  • Some online postings mention to connect the heater core with the inlet on the top, I followed the factory configuration with the inlet routed to the bottom and the outlet on the top of the heater core. This configuration also works best to push air out of the heater core.
Antifreeze
  • Research on antifreeze lead me to Zerex G05 50-50 to support both the aluminum radiator and heater core.
 

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Or make your own tubes from some thinwall stainless tubing and some boy racer red/blue AN fittings. This is my FFR Cobra I built back in 2008 or so. I'm doing something similar on my current build, just not with the red/blue stuff.
 

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Hmm...nice job.

Ran into the same issues (somewhat) doing a 5.0 conversion using the OEM heater tube assembly. An FYI for 'ya, there's an o-ring in the swivel assembly where you attach it to the intake that can leak eventually. However, the o-ring is replaceable. You have to take the tube assembly out of the car, "deswedge" the fitting (I just used a crescent wrench and spun it around the flare while cranking in on it every could of turns until I had reduced the diameter of the flare to the point the swivel could be disassembled. The o-ring is a 10 cent hardware store o-ring available anywhere. Replace, reflare, reinstall.

Phil
 

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Not the best picture, but I ran (2) lines of thin-wall stainless with (Swagelok) hose barbs welded to each end, each line welded together with small tabs that also lined up with a couple of my exhaust mounting bolts. I then spent a bunch of time combing the heater hose manufacturers catalogues to find (4) hoses with the perfect bends (or a section). I love the cleanliness of it, plus it stays away from my tri-power linkages
IMG_5344.JPG
.
 

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I wanted to do this combined with the heater core that has extended barbs into the engine bay. I hear they're aluminum and they are "crap." Thoughts on this?
 

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I like how it's clean, but do you think you'd have room to install a heater control valve in-line somewhere?
What did they do in late model cars using these tubes?
 

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Discussion Starter #10 (Edited)
I wanted to do this combined with the heater core that has extended barbs into the engine bay. I hear they're aluminum and they are "crap." Thoughts on this?
I looked into this and carefully considered it. In the end this seemed to boil down to three points which I mention in the post.

Excessive water pressure: Especially on higher performance engines, the inlet tube should be smaller (5/8") than the outlet (3/4"= 6/8") in order to keep fluctuating water pressure due to changes in water pump RPM 'in check' so that it doesn't blow out the core. My hard line was already different diameters for inlet/outlet so by design this was in check. You can also purchase an inline flow restriction insert to accomplish the same (part number is listed in the post).

Metallurgy: My understanding is that having mixed metals in the cooling system can cause premature decay, in particular reactions between aluminum and copper. Because my cylinder heads and radiator are already aluminum the copper in my equation is reduced with the addition of an aluminum heater code.

Coolant: Next is to add a coolant that is aluminum compatible and also is premixed. The premix part is important because it removes two other sources of error in premix dilution/concentration ratio and the introduction of other mineral contaminates to the system from the addition of tap water that can reduce the corrosion properties of antifreeze/coolant. Rather than purchase distilled water and go through the hassle of premixing I just went with the premixed Zerex G-05 which is also listed as playing well with aluminum.
 

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I don't think these days they sell a coolant that DOESN'T play well with aluminum. I like the -P-HOAT "for" Nissans as it's a pretty blue color. gnsh above mentions G-05 which is plain HOAT for late model Fords (and others) but is not as optimal for engines with cast iron blocks like the phosphated versions. It's essentially the newest version of GM's famous "Dex-Cool" and is a pee yellow color.

If you want to go anal technical about the life of your heater core you might want to look into minimizing electrolysis i n the system. In some systems you can even measure voltage in the coolant as the acids in it (ahem, not pointing any fingers, but Dex-Cool) can in effective make the cooling system like a wet cell battery. A few years ago this was eating many a GM heater core from the inside out. It was weird and a prolific problem. Put me off using Dex-Cool, not that I was terribly fond of it. Full disclosure, the early Dex-Cool that caused things like Saturn to scrap a few hundred brand new cars right on the factory lot isn't the same as what they sell now. You could call it "Dex-Cool II", it's a pretty different formulation.

I like aluminum heater cores. I've had it proved to me empirically that an aluminum one can put out a LOT more heat than a brass one. All things being equal. The problem is like with all other auto parts, you have to find a buy a good quality. A crappy aluminum one is no better than a crappy brass one. Anyone remember the big run of crummy brass heater cores that had us replacing them every six months or so? Some wouldn't even last a week.
 

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Im toying with no heater at all. Down here in the South its only needed a few days a year anyway.
 
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