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Technical Y Block Heater Plumbing Question

Discussion in 'The Hokey Ass Message Board' started by AVater, Mar 9, 2026 at 3:50 PM.

  1. AVater
    Joined: Dec 9, 2008
    Posts: 3,521

    AVater
    ALLIANCE MEMBER

    I’m looking to connect my heater on my project correctly. Need advice on which hose goes where on this Y Block engine. One hose goes from an outlet on the intake manifold and the other from an outlet on the p***enger side of the water pump. Which of these would be the “hot” water source for the heater? Which hose goes to the upper heater outlet tube and which to the lower heater outlet tube?
    Thank you for your help.
    IMG_6524.jpeg
     
  2. chicken
    Joined: Aug 15, 2004
    Posts: 701

    chicken
    Member
    from Kansas

    The fitting on the manifold is the HOT one. I'd probably hook it to the lower one on the heater but Ford may have had other ideas.
     
  3. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 16,354

    Bandit Billy
    ALLIANCE MEMBER

    Sounds like the rooster caught up with ya when your back was turned.

    The hot water inlet line needs to be the one that is turned off by either an external heater valve or the internal valve in the heater box. If it doesn't have one, the heater likely won't know which hose is routed where. All cars should have one to keep the heater from warming the interior during summer.
     
  4. AVater
    Joined: Dec 9, 2008
    Posts: 3,521

    AVater
    ALLIANCE MEMBER

  5. Yes, the intake is the hot water supply. The valve you have installed is the 'cheap fix' instead of the somewhat expensive vacuum valve Ford used as OEM... https://www.ebay.com/itm/1277179461...MI5q2R-4OUkwMVeNXCBB1SBhw-EAQYAiABEgLd2PD_BwE
    And unfortunately, that's only part of it. There's another vacuum valve located under the dash at the heater that gets its vacuum source from the wipers, this is where the cable from your temp control lever connects. This had a hose that went to the manifold valve and opened it under command from the under-dash valve. They were known for diaphragm failures and leaking. At one time not too far in the past, that manifold valve was unobtainium, the valve you have now was the usual answer. The problem with these is they tend to leak pretty good if they're not fully closed or fully open, so its full heat or no heat.

    Ford also offered a 'base' heater (up until the late '60s on various vehicles, rarely seen) that was operated with one knob. Pushed in, no heat. Pulling halfway out got you heat, all the way was defrost. You turned the knob for the fan. No temp control at all, Ford owners manuals recommended opening a window... LOL. That's what you'll be doing...
     
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  6. y'sguy
    Joined: Feb 25, 2008
    Posts: 819

    y'sguy
    Member
    from Tulsa, OK

    On my 55 Bird I use a br*** elbow at the intake manifold. That hose then connects to a valve that is controlled by the original heater control on the dash with a cable connect. It works reasonably well and is much cheaper than the original style valve on the manifold. It mounts inline in the hose. Out of site. Available from most T-Bird supply houses. Although I think it is originally a Mopar part?

    You may be able to take this pic of the valve to a local parts house and have them match it up. (if they are any good!)


    upload_2026-3-9_21-39-2.png

    upload_2026-3-9_21-34-22.jpeg
     
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  7. BJR
    Joined: Mar 11, 2005
    Posts: 11,523

    BJR
    Member

    That cable operated heater valve is what is used on a 1975 Dodge pickup trucks.
     
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  8. y'sguy
    Joined: Feb 25, 2008
    Posts: 819

    y'sguy
    Member
    from Tulsa, OK

    Good to know, I thought I had heard something like that, Thanks!
     
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  9. jimmy six
    Joined: Mar 21, 2006
    Posts: 17,325

    jimmy six
    ALLIANCE MEMBER

    All Fairlane models I ever saw had vacuum operated valves on the intake. The 2 lines went to the fire wall near the fan to the heat exchanger/mini radiator in the under dash unit it actually made no difference which hose went to the fittings extended from the fire wall. I just kept mine parallel. The basic heater had a manual valve on the intake and the 2 hoses went to a different spot on the firewall above the distributor. They made no difference either so you attached to look the best.
    You manually shut off the valve in summer to keep the coolant from recirculating thru the p***enger compartment. The vacuum style valve did this for you.
     
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  10. The '50s era Ford 'Magic Aire' heaters were actually fairly trick for the times. The under-dash valve did two things: it modulated the manifold valve to allow water flow through the heater core, but it also had a bi-metal temperature sensor that would maintain the 'set' temperature of the water going through the core for more precise control. Most other heaters mixed hot/cold air via a duct flap to set temperature, and variations in engine and ambient temps caused the set temp to vary widely, allowing larger differences for a given set point.

    While the early versions (up to '57) used the manifold control valve, '58-up consolidated both functions to the under-dash valve, so a simple elbow was used at the engine. If you ever had a '58 or newer Ford 'Magic Aire' heater that wouldn't heat, make sure the vacuum connection to this valve is in place or no heat. I froze my *** off for most of one winter before discovering this... If I revved the motor to 6K RPM, the increased water pressure flow would force the valve open momentarily, producing a 'squeak' noise and a short blast of warm air.

    Ford discontinued this design sometime in the '60s, I guess they figured the expense wasn't worth it. AFAIK, the '58-up units were more reliable.
     
    Last edited: Mar 10, 2026 at 2:06 PM
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  11. Mr48chev
    Joined: Dec 28, 2007
    Posts: 36,148

    Mr48chev
    ALLIANCE MEMBER

    Hot water "OUT" usually close to the thermostat as on the manifold . Return "INLET" on the water pump same as the inlet hose from the radiator. The heater core being just a smaller radiator.
    Another easy to find cable operated heater control valve is the one for Broncos and some F series Ford Trucks . This image simply because it has a good picture and shows what vehicles it fits for searching purposes. Plus it has the clamp for the cable housing. Some regular parts houses only stock a plastic verson though . Screenshot (2820).png
     
  12. y'sguy
    Joined: Feb 25, 2008
    Posts: 819

    y'sguy
    Member
    from Tulsa, OK

    Yeah, that's similar to the one I have.
     

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