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A4 B6 - Mystery Coolant problem

Euangray Oct 8, 2018

  1. Euangray

    Euangray New Member

    Hi, having a bit of a weird one with my ageing but fairly low milage (59k miles) A4, 1.8T avant quattro.

    I'm at a loss, so hoping someone can help out:

    Its been leaking coolant slowly for a while, but never more than a couple of drips in the driveway. Then one day, sitting in a hot traffic jam, the thermostat housing exploded in a pile of steam and left me stranded. I got towed home, replaced the housing and refilled the system to max.

    Worked fine for a week or so... Now, if i'm driving for more than 30mins, the coolant light flashes up. I stop, look under the hood, the coolant level is sitting well below the min line. I loosen the cap, it hisses and fills back up, but not to the max line. The breather pipe appears to be unblocked, as it lets coolant spill out the back of the expansion tank if you overfill it.

    Additionally, now when i put the cabin fan on to demist the windscreen, it puffs a load of steam up the inside of the windscreen. It clears after ten seconds, but obviously this is not ideal when driving...

    Took it to the garage, they had the system pressurised for two hours, couldnt find a leak, but said the fan control module was showing an intermittant fault. I cant see why this would be causing the symptoms above though.

    To me, it seems like the coolant system might be leaking internally, somehow getting into the cabin heating system, but having not dug into those areas that's a complete guess. Anyone come across something like this before.

    Grateful for any pointers,

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  3. S4_dan

    S4_dan Fire up the Quattro! VCDS Map User

    Could be heater matrix leaking. Not too bad of a job on the B6 models.
    Worth having a look in drivers footwell and removing the trim to access the matrix. If it's wet then could be your problem.
  4. jbcalvin

    jbcalvin Member

    I had something similar to this a couple of years ago, ended up being the head gasket starting to fail, only happened once car was fully warmed up, thermostat open and system fully pressurised, replaced and no problems since then.......

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