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Bleeding 1.8T cooling system

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by Marcos M, Mar 13, 2009.

  1. Marcos M
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    Marcos M Member

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    [Mar 13, 2009]
    Hi guys
    Thought I'd try this here as I'm not getting any response on the tech forum.
    Just got my first Audi a B6 1.8T QS and it's pretty good, however, I bought the thing with a duff thermostat which is now replaced and the problem solved but I can't seem to get the coolant system to bleed properly, Heater does not blow hot until the engine is above about 3000 rpm then it works perfect I've bled it threw the screw on the coolant pipe and through the hole in the heater hose with the engine running and heater on HI but still it only blows cold at idle.
    Any ideas or suggestions most appreciated
    cheers
    Marcos
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  3. evilscotsman
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    evilscotsman Space Cowboy

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    [Mar 15, 2009]
    I have a coolant flange leak mate, and mine does the same. Here are some top tips.

    With the cap off and the engine running, keep the water at the top of the little posts inside the filler on the expansion bottle, set the cc to HI inside and watch the bottle, as the engine circulates the air it will come out of the bottle pushing water out too.

    Rev it sometimes and keep the water topped up, when all the air is out it will settle down and stop surging over the top (at idle) - it takes a few minutes to get all the air out. If using the bleed screw, you need to top up the bottle while it bleeds for about 10 minutes as the bleed screw is small, but just using the bottle as the escape is fine, you lose more water, but it bleeds quick and the heat will work. Theres a down-hill run on the last return pipe, thats what traps the bloody air in the system.

    If you go to a plumbers merchant - heres a wee gadget to make bleeding easier.

    Get a 1/4" to 6mm compressed air fitting with the push-in end (blue ring) - they will know what you mean - and a length (3') of the 6mm plastic airline tubing to go with the fitting, then screw the fitting in place of the bleed screw, put the end of the pipe in the top of the expansion bottle, and let it bleed merrily away with no water loss!

    When its just water circulating, switch off the engine, let the water level settle and unscrew the fitting & pipe, then refit the bleed screw, the water will just sit at the top of the bleed screw hole and no air will get in, put the top on the reservior and your done.

    (about £3 in parts)

    NOTE: dont put the water higher that the tops of the little posts in the expansion bottle, or it will create a hydralic lock and the heat will be poor, there has to be some expansion space above the water for the system to work properly.

    I'll post pics of the bits if you cant get what they are :)
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  4. Marcos M
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    Marcos M Member

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    [Mar 15, 2009]
    Thanks for the reply mate, I've got the bits you talk about in the garage I'll give it a go. cheers.
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  5. evilscotsman
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    evilscotsman Space Cowboy

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    [Mar 15, 2009]
    np :)
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