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  1. #1
    Established Member Two Rings
    Join Date
    Nov 08 2016
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    384994
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    Big Sky

    Heater Core Hose Swap

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    If I switch out my heater core hoses do I need to drain coolant? Would I then have to bleed the system or can I just reattach the hoses, run the car with the heat on and add coolant as necessary?

  2. #2
    Veteran Member Three Rings
    Join Date
    Jun 07 2005
    AZ Member #
    6784
    Location
    Shepherdstown, WV

    Yes, you can either drain it controlled at the radiator or you can make a mess when you pull the hoses at the back of the engine and let it drain on it's own then, no getting around draining.

    Since the top of the heater core hoses are the highest part in the system you will need to bleed it. There is a hole in the hose to allow air out that will get you most of the way but you'll likely need to top it off a free times after doing it until it fully bleeds. Alternatively you can vacuum it and then it sucks up coolant and fully fills automatically. Never had to bleed a car using a vacuum filler, it's one of the best tools ever invented.

  3. #3
    Established Member Two Rings
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    Nov 08 2016
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    384994
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    Big Sky

    Thanks. Do you know how much coolant will drain from the hoses vs. lower radiator

    Quote Originally Posted by chris86vw View Post
    Yes, you can either drain it controlled at the radiator or you can make a mess when you pull the hoses at the back of the engine and let it drain on it's own then, no getting around draining.

    Since the top of the heater core hoses are the highest part in the system you will need to bleed it. There is a hole in the hose to allow air out that will get you most of the way but you'll likely need to top it off a free times after doing it until it fully bleeds. Alternatively you can vacuum it and then it sucks up coolant and fully fills automatically. Never had to bleed a car using a vacuum filler, it's one of the best tools ever invented.

  4. #4
    Senior Member Two Rings ShelbyM3's Avatar
    Join Date
    Feb 05 2007
    AZ Member #
    15417
    Location
    Portland, OR

    When I replaced my heater core I drained from the core itself in the driver’s footwell. Like said above, the heater core lines are the highest point in the system, so if you drain from the engine side there will still be a decent amount of coolant in the core itself. I used a flexible plastic container and snuck it under the coolant lines next to the gas pedal. I made a little mess, but had a rag under there and my carpet dried out relatively quickly. I got roughly a quart or so of coolant out that way. Made sense to my brain, but may not be the best method.
    Also, be prepared to fight with the hard lines on the core itself. The clamps are a total pain to reattach. That was the longest part of the job for me.


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  5. #5
    Veteran Member Four Rings
    Join Date
    May 09 2012
    AZ Member #
    93306
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    08 A4 Avant, 05 Silver S4 2.7t swap
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    Are you talking about the rubber ones in the engine bay or the hard pipes behind the dash that go to the core? If you have a set of rubber hose clamps you can minimize drainage by using those on the rubber hoses. You should lose a lot. Just throw a towel down in the firewall under the hoses. You will need to bleed the system as mentioned. There is a hole in one of the hoses. Put it on so that it is not all the way on over the metal fitting. Turn the car on and run it until coolant starts to leak out the hole. Then slide that hose back on and replace the clamp.


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  6. #6
    Senior Member Two Rings ShelbyM3's Avatar
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    Feb 05 2007
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    15417
    Location
    Portland, OR

    Quote Originally Posted by jbain2 View Post
    Are you talking about the rubber ones in the engine bay or the hard pipes behind the dash that go to the core? If you have a set of rubber hose clamps you can minimize drainage by using those on the rubber hoses. You should lose a lot. Just throw a towel down in the firewall under the hoses. You will need to bleed the system as mentioned. There is a hole in one of the hoses. Put it on so that it is not all the way on over the metal fitting. Turn the car on and run it until coolant starts to leak out the hole. Then slide that hose back on and replace the clamp.


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    I guess I immediately thought of the hard lines. If it is the rubber hoses behind the engine, drain from the firewall and bleed as described above. Piece of cake.


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  7. #7
    Established Member Two Rings
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    Nov 08 2016
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    384994
    Location
    Big Sky

    Yup It is the two rubber ones that go through the firewall. Both look to be leaking at the back of the engine where the black plastic connection meets the rubber hose.

  8. #8
    Senior Member Two Rings ShelbyM3's Avatar
    Join Date
    Feb 05 2007
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    15417
    Location
    Portland, OR

    While you’re at it, it may not be a terrible idea to flush your heater core, if you haven’t it any attention. They’re notorious for clogging up.


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  9. #9
    Veteran Member Four Rings
    Join Date
    May 09 2012
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    Quote Originally Posted by ShelbyM3 View Post
    While you’re at it, it may not be a terrible idea to flush your heater core, if you haven’t it any attention. They’re notorious for clogging up.


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    For sure do this. Several different ways people have done this.


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