Touran 1.4 TSI smoking from exhaust - but only sometimes?

[andre_xs]

Dear All,
We have a Touran 1T from 2010, 140 TSI petrol engine with supercharger and turbocharger and 7-gear DSG.

The car is using up oil quite a bit and the exhaust always smells a bit like burned oil.

However, our main issue: It *sometimes* smokes (blueish) from the exhaust like crazy. Like "Police will stop me immediately" and cars keeping their distance. But then again for days of driving no visible smoke at all. I haven't found a systematic pattern yet when it smokes and when it doesn't (I pay a lot of attention to whether engine is cold or hot, stood for a while, running in idle for a while, driving gently or really pushing it in sport/manual mode, having the motor push (e.g. downhill, motor break).

I can't reproduce the smoking, it seems to appear fully random.

What kind of error could cause such a behaviour? Looks like something does seal the oil well enough most of the time, but sometimes not very well (smoking), and then again. What engine part could that be?

Best wishes,
Andre

[andre_xs]

forgot to mention that compression was tested, these are the values:

Engine hot:12/12/11.5/11.5 bar

Engine cold::10.8/11.5/11/10.5 bar

To my (very limited) knowledge they are not brilliant but still fine.

[GreenV8S]

Two obvious potential candidates are valve stem oil seals and turbo oil seals. Either of those could cause intermittent oil leaks that would end up in the cylinder.

[paul_c123]

And a third obvious candidate is the rings are f***ed. The reason it may result in intermittent smoke is the crankcase pressure could be varying, depending on what the crankcase ventilation system is doing. A cylinder leakdown test is quite cheap/easy to do and will give useful direction.

[andre_xs]

Thanks to both of you, will look into that.