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Coolant leak ABY Avant

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  • #16
    Why don't you put some pressure in the system and see where it leaks?

    0.5-1 bar should be enough to find a leak. Just disconnect the overflow hose at the expansion tank and plug it. Then put a little pressure in the expansion tank and see where it leaks.
    Sleeper S2 Avant +450

    A6 Avant 2.7t Stage 3

    Audi S2 Coupe RS2'ed

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    • #17
      So not really had much time with the car recently but not sure I am actually losing coolant. The main problem seems to be the fluctuating level in the expansion tank. I've been through the guide on here to bleed the coolant system but not really sure what the issue is - an air lock somewhere? At no point has the car been overheating and no low coolant warning (not sure what the threshold is here?).

      Basically the coolant level behaves in the exact opposite of how it should. The car will be at min mark when cold but drop when warm rather than increase - the level returns back to min once it's cold. I went out this morning and bled the coolant system again using the radiator bleed valve to release the pressure and all seemed well. Drove for about 30 mins and again coolant level had dropped. I let it cool for a bit and then removed the header tank cap. I then fired up the engine and it immediately jumped up to between min and max then again dropped back to min once cool - as it should. Another 30 min drive after that and it's back below min mark...

      I did notice looking through pictures of when I first bought the car the level was already low - think I missed this due to the min marker being much lower on the V6 saloon - basically where the coolant level was on the S2 - so I assumed at a glance this was the correct level.

      Surely if there was a leak it would continue until there was no more coolant? The level never gets lower than about an inch and a half below the min marker.

      The car is running great otherwise and while this doesn't seem to cause any problems it's bugging me

      Any ideas guys?


      93 S2 Avant
      94 80 V6 Saloon

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      • #18
        Originally posted by Jonas_R View Post
        Why don't you put some pressure in the system and see where it leaks?

        0.5-1 bar should be enough to find a leak. Just disconnect the overflow hose at the expansion tank and plug it. Then put a little pressure in the expansion tank and see where it leaks.
        Cheers. I've ordered a kit so will check do a pressure test next week.

        93 S2 Avant
        94 80 V6 Saloon

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        • #19
          If you’ve got a small leak at the turbo causing the bubbling, or somewhere else low down, maybe it draws air in as the system cools..

          S2 Coupe 3B Project


          Ur quattro restoration

          S2 Avant

          Boost is the new rock and roll!
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          • #20
            Originally posted by newsh View Post
            If you’ve got a small leak at the turbo causing the bubbling, or somewhere else low down, maybe it draws air in as the system cools..
            Yeh, that could be it. It's a small leak but it's clearly leaking from there. Either way it makes sense to sort that before looking at anything else.

            Had a better look today - putting pressure in the system holds fine but does make the leak look a lot more obvious when it's cold. Lost about 0.1 bar in about 15 mins so leak is minimal. You can see it starting to pool at the bottom of the coolant return pipe.

            oFLGGvb.jpg?1.jpg



            Jw5HGbT.png
            I'm guessing it's the o-ring that's perished? Number 6 on the diagram. Shouldn't be too difficult to replace.
            Last edited by Steve770; 13th August 2019, 22:54.
            93 S2 Avant
            94 80 V6 Saloon

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            • #21
              Looks like a copper washer, might just need tightening.
              Try slacking the union nut, tighten the adapter down to crush the washer a bit and then retighten the upper nut.
              You might want to anneal the copper washer first though by heating till it glows and quenching in water.

              S2 Coupe 3B Project


              Ur quattro restoration

              S2 Avant

              Boost is the new rock and roll!
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