How To Bleed Cooling System
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  1. #1
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    How To Bleed Cooling System

    Hi all. I've been having a "gurgling" sound coming from my heater core on a regular basis. It seems to be a little worse first thing in the mornings but is fairly consistent. I just replaced my coolant temp sensor this morning which works great now but the gurgling sound seems to be a little bit worse. What is the proper procedure to bleed my cooling system? I have a 2000 1.8T ATW. Thanks!

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  3. #2
    Super (Charged) Moderator, Grinding Gears...gone fishing! ScottPassat2.8's Avatar
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  4. #3
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    Thanks Scott. I tried this last night with no success. I did the procedure until it was bleeding coolant steadily out of the hole. This happened fairly quickly. This morning when I started the car up it made the exact same gurgling noise which I can almost guarantee is still air stuck in the heater core. I think the coolant line before the bleed hole (and heater core) is free from air but I need to somehow get the air out of the core which is after the bleeder hole. Is there any other bleed screw just after the core which I could use? Any help would be appreciated...

  5. #4
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    the coolant reservoir is the bleeder also. You can also run the engine with the coolant reservoir cap off-- to see if it makes a difference

  6. #5
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    The bleeder is on the outlet of the core.

    I've found these cooling systems to be pretty self-purging even if you don't even bother with that bleed hole.

    The coolant pump that runs for 5 minutes after the engine shuts off will also do it.

    I suspect you've got a leak somewhere.

  7. #6
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    Quote Originally Posted by 50pascals View Post
    The bleeder is on the outlet of the core.

    I've found these cooling systems to be pretty self-purging even if you don't even bother with that bleed hole.

    The coolant pump that runs for 5 minutes after the engine shuts off will also do it.

    I suspect you've got a leak somewhere.

    Yep - I still have that sound coming from the core.... Any other tips? FYI - my car does not have the secondary coolant pump which runs after shutting off the car.

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    Super (Charged) Moderator, Grinding Gears...gone fishing! ScottPassat2.8's Avatar
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  9. #8
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    Quote Originally Posted by scottpassat2.8 View Post
    What ^ he said. I had what I thought was an air bubble in the core because I could hear some gurgling noises. Turns out this was flow noise caused by all of the contaminants restricting the passages. My shop was able to flush out "a bunch" of sediment and the heater has been working great for the past year.

  10. #9
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    Search for my thread on flushing the heater core.


    I got alot out, but nothing compared to blowing it out with air. And it will probably keep reclogging.

    Oh, another quick test for clogged heater core. Once car is all warmed up, feel the hoses. One is obviously very hot - assuming at least a little coolant flow. The other hose should at least be very warm. If it's cold your core is clogged.

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