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Small leak under expansion tank

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by tomyoud, Mar 15, 2014.

  1. tomyoud
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    tomyoud New Member

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    Hi guys, got a slight problem with my 2008 Audi A4 Avant 1.9 TDi.

    I've noticed it to be damp/wet directly under the expansion tank cap and dripping down to the bottom of the engine. I've lost the difference between the max and min mark in just over three months. I've heard there is a drain somewhere on the underside of the tank and releases if there is too much pressure. Could this just be that I need to get a new cap?? Or the tank needs replacing??

    The car drives fine, no change in performance at all and the coolant is the nice pink colour and is very clean (had it change in a service 4 months ago) and I can't think it could be the head gasket that's gone otherwise I'd gave oil in the coolant or vice versa but I have neither....I think

    Any ideas would be greatly appreciated.
    Last edited: Mar 15, 2014
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  2. lukey baby
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    lukey baby Member

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    Get the system pressure tested to see if there are leaks
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  3. lynallbel
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    lynallbel Active Member

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    Cap is always first port of call, most have some sort of pressure relief built into them and this normally vents out the centre of the cap down through the expansion tank.
    Check first as yours may be different, but cap is always cheapest place to start, plus if its taking 3 months to drop the level its not likely to be the head gasket.
    #3
  4. tomyoud
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    tomyoud New Member

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    Thanks for the reassurance. I was really hoping it wouldn't be. I've ordered a new cap and also getting it pressure tested just to make sure it's nothing else.
    I'll post the results tomorrow
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  5. tomyoud
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    tomyoud New Member

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    Ok, turned out I had a crack in expansion tank (next to the overflow drain). Audi very kindly replaced it and diagnosed it for free for as they did a pressure test a month ago and found the thermostat housing had a slight leak and thought they would have been able spot it at the same time....especially when I've done less than 100 miles since it was there.
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  6. lynallbel
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    lynallbel Active Member

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    Well you cant get cheaper than that!
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