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  1. #1

    Default What to use to bypass a heater core on fuel injected Mustang

    I have a 1990 Mustang 5.0 LX convertible with 16,000 original miles, and radiator started leaking, had redone. Due to age deciding to bypass heater core, before it leaks, while apart, everything about bypassing it looks the same as if I do it on my 86 Gt. I understand you probably can probably only bypass it at the back of the intake manifold and use something to make the inlet pipe go back though outlet pipe, but what have you used as the new heater hoses i have one is 5/8" and one is 3/4" inside diameter and the heater pipes behind intake are so close together. I don't want to do anything to permantlly alter car, but i don't want a heater core leak, and don't ever run car when heat is needed. Any help would be very appreciated, unfortunatly the heater core repacement and bypassing of them isn't nearly as easy as my 67 Mustangs are. Thanks Keith

  2. #2
    FEP Power Member
    Join Date
    Nov 2007
    San Mateo, CA


    I plan to put a plug in the heater hose on my wifeís car. I will be ordering some temperature compatible plastic stock. Using a plug inside the hose allows it to be hidden.

    My wifeís car is a trailered show car so no rush to fix it. Looks like I have 3 heater cores on my to do list. Iím in no rush to do them. I have 2 replacement Ford heater cores on hand.
    Last edited by KevinK; 06-01-2020 at 03:10 PM.
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  3. #3


    They make hose adapters / connectors that are two barbed ends. You can get them in multiple sizes and either for matching hose sizes or reducing/enlarging.

    I had to find them when I put the SEFI 5.0 in my 1981 F150. My heater core used 5/8 in 5/8 out hose and the 5.0 was 1/2 / 3/4.

    I believe they were from NAPA but could have been the local hydraulic hose company.


  4. #4


    I've always found larger Ace Hardware stores to be well stocked for fittings which you'll find in their plumbing section. The bigger ones have about 6 barn door style panels that are 4x8 with tons of variations. Their staff is really helpful. Any exposed part can always be painted block or covered with a piece of black corrugated electrical wiring wrap. Worst case check out. Summit

    1983 Mustang GT
    Popular Hot Rodding Project Car '83/84

  5. #5

  6. #6


    Great info
    79 Zephyr, 4v/4r70w swap planned, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs.

  7. #7
    Moderator wraithracing's Avatar
    Join Date
    Jun 2010
    Grand Junction, CO/RR TX


    I believe this is what you want and need to by-pass the heater hoses on the engine. This should be 5/8" on one end and 3/4" on the other. You will need to trim to fit, but this should look the heater lines. Double check my information, but that is what I show. I might be wrong, but hopefully not!

    You may be able to get your local auto parts store to order or cross the Dayco number. Good Luck!

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  8. #8


    I did this to my 86 today due to my heater core springing a leak a couple days ago. I removed the heater tube entirely, plugged the lower outlet on the water pump and used a 1/2" to 3/8" NPT reducer to install the ECT directly into the intake. Looks clean and frees up some space.

    1986 Mustang GT 5spd
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  9. #9


    I have had 2 of the plastic connectors fail. Advance has this one in stock(At least they did at my store):

  10. #10


    Thank you very much for the info. Am I correct about bypassing it at the end of the heater pipes at the back of the intake manifold where the inlet and outlet hoses going to heater core would hook up? I cross referenced number and apparently Gates # 18473 is the same, I ordered through local auto parts store which only has locations in the county I live in. Hopefully it will work out. Thanks.

  11. #11


    So you are just putting plug in inlet and outlet hoses going to heater core at firewall. If you can tell me what you get and where from when you get it from when you get it. I am assuming as long its a real tight fit, no coolant would get through. Thanks.

  12. #12


    I used a 90 degree elbow to bypass mine.

    All I can say is I put the restrictor in too late — again

  13. #13


    CJ Pony parts has owed me a flow restrictor for months now
    i hope it gets here soon lol
    79 Zephyr, 4v/4r70w swap planned, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs.

  14. #14
    FEP Power Member mcb82gt's Avatar
    Join Date
    Jan 2004
    Olathe, Kansas


    Quote Originally Posted by massacre View Post
    CJ Pony parts has owed me a flow restrictor for months now
    i hope it gets here soon lol
    Use a properly sized socket.

    Now stang-less.

    88 Cougar 5.0

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