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Disappearing Water??

Discussion in 'A4/S4 forum(B5 Chassis)' started by norad97, Sep 6, 2010.

  1. norad97
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    norad97 Member

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    My Temprature gauge has been playing up latley, dropping back to Zero
    then back to normal.
    I also noticed my water has been going down, topping up but still goes down to minimum after
    a week.

    I was thinking of changing the temprature sensor first, but talking to a chap who had an S3,
    he said he had the same problem, changed the sensor but still faulty, it was the themostat??

    I cannot find where my water is going?? I took the undertray off and run the car hot, but still cant
    find it,, although the tray shows a white water mark on it, on the front left side!!!

    anyone had this problem??
    #1
  2. Blue_Thunder
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    Blue_Thunder Active Member

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    Do you get white smoke from the exhaust?

    Also, what are you topping your coolant up with??
    #2
  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Our old car would go down to minimum then stay there, so i gave up and just left it at minimum.

    If the guage is being erratic then its more likely the sensor, dodgy thermostat will usually just mean it never gets to 90, or if it does, it'll drop back when your driving at high speed, like on the motorway.
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  4. norad97
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    norad97 Member

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    Hi, I always top up with the correct coolant and now white smoke from the exhaust.

    The Gauge reaches 90, but can drop back and then go back and stay there,
    Why would driving at speed on motorways affect the thermostate????

    and where is the water going??
    #4
  5. evilscotsman
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    evilscotsman Space Cowboy

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    rear plastic coolant flange will be cracked at the back of the engine, costs pennies but you cant get near it without taking some bits off.


    It drips onto the hot parts and vapourises but leaks a bit when its cooling down so you get a wee bit of water staining. Bet your heaters dont blow hot either unless you rev the engine quite high?
    #5
  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Heater was fine on mine.

    Dont think the B5's have the same issues with those flanges comapred with the B6.
    #6
  7. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    I presume thats supposed to read "no white smoke"?

    If the guage drops from 90 the stat is broken. The stat controls the water flow thru the radiator. Once the engine reaches operational temperature, it opens and allows water to flow round the radiator, and it adjusts the amount its open by continuously to ensure the water stays at 90c. When your on the motorway, you tend to be driving at high speed, so lots of airflow thru the rad, but without all that much engine load, so low amount of heat generated. When the stat gets old it doesnt control the water flow properly, and can allow too much thru to the radiator, allowing the temp to drop below 90c.

    Add to this that the guage has a built in buffer, and shows 90 for any temp from about 80c to 100c, so if the guage is dropping its cooling off by a fair amount.

    As for where the water was going, the old car had pink crust round the radiator end tanks, so i suspect it was seeping from there. With the reservoir full, the coolant system will be under more pressure, so its more likely to leak.
    #7

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