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Water pump failed, how do you diagnose it properly?

Boro&Beth Jun 27, 2009

  1. Boro&Beth

    Boro&Beth Member

    Ive read a few topics and i think our S3 needs a new one, even though the last one was replaced in 2006, 35k ago.

    A friend of ours doesnt think it is the water pump, so is there a definitive way to test/check to see if its failed/failing?

    Symptoms are:-

    Doesnt overheat on tickover no matter how long its left running.

    Doesnt overheat while driving below 2000rpm in any gear, so is happy to cruise along at 50mph in 6th.

    Only overheats at revs more than 2000rpm and then coasting in neutral will soon bring the temps back down again.

    Fans are working ok, so not a fuse. Water levels are good too.

    Some people have said look for a "jet of water" in the expansion bottle.

    Here's a video (we added an extension tube to make it clearer).

    Is the jet as strong as it should be?


    Seems to have a steady flow on tickover, increases when the revs rise, then dies down again when revs rise further. Im not 100% sure this will help diagnose as i know it doesnt overheat on tickover even when revving constantly at 3000rpm.

    Any tests we can do?

    Any help appreciated.
  2. Essflee

    Essflee Well-Known Member

    I wouldn't have thought that the water pump was at fault either, going on previous experience when my A3's water pump went I couldn't drive the car, would over heat quicker if anything when sitting still...

    Could be a thermostat problem instead, or temp sender, I wouldn't think the pump...but I maybe wrong.

    The pump must be working if the car doesn't overheat when stationary, bit of a strange one:think:
  3. Boro&Beth

    Boro&Beth Member

    We just recently had a new thermostat. Vag.com isnt showing any temp sender faults but not sure if it should anyway. Might be worth replacing anyway as a cheap possible fix.

    I was just wondering if the plastic impellers werent that damaged it may act oddly at speed?
  4. Essflee

    Essflee Well-Known Member

    I suppose that's possible, can handle the engine at tick over but as the pressure builds the pump can't take it... You could be right !
  5. AwesomeSarah

    AwesomeSarah Member

    Yes what happens is part of the impella breaks off
    When going steady or ticking over , the part of the impella that is left can manage to pump round the water
    Then if you go faster , motorway speed the rest of the impella`s cant cope and then will start to overheat
  6. Boro&Beth

    Boro&Beth Member

    Booked in for a new one and cambelt.

    Thanks for the advice
  7. voorhees

    voorhees Moderator Staff Member Moderator Team V8 Audi S5 s tronic

    if you remove your thermostat you can see the impeller to check IIRC
  8. Caesium

    Caesium My BM is fixed! VCDS Map User

    That hose in your vid should be literally gushing with coolant, its normally a thermostat bypass to avoid excessive pressure build up.
    I'd say your impeller is either adrift or has lost some fins, either that or there is a blockage somewhere.
  9. b16 will

    b16 will Member

    The impellor comes away from the shaft, it spinns at low revs but cannot keep up higher up the rev range, ive done 3 or 4 like this.

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