Random smoking issue

[Antsa]

Hello all

Lately my S2 has been suffering from occasional smoking. It annoying because I have not found anything that would clearly point me the reason. Here is what happens:

- never smokes when started cold
- seems like smoking happens when engine is under vacuum (lightly cruising)
- no smoking under boost

I did change the oil from 10w50 to 10w40 in the spring but it has been fine until now. Could the less viscous oil be the cause? I know that worn rings, bad valve stem seals, crankcase ventilation system and leaky turbo seals can cause smoking problems. What would be the best way to proceed and how to verify/rule out the possible causes of the smoking?

Thanks in advance

Antti

[Bowie69]

I'd start by pulling the inlet tract apart looking for oil.

Oil near turbo = turbo
oil near breather = possibly rings

Tbh smoking at light throttle sounds like turbo.

Other options are head gasket of course, as well as rings (possible) or guides (unlikely as doesn't smoke after cold start).

[Ian Simmonds]

Before we replaced the turbo on ours it smoked.... Easy to identify as the turbo oil seal leaks-by as it warms up or (as said) light throttle. Start it up from cold and don’t touch it.... After about 5 minutes if you can see more than 5m it’s not the turbo. Ours, seriously, I used to fumigate the spiders out of the garage with that technique.

[Antsa]

Let the car idle today for 10min and no smoke at all. Will have to check the intake for oil traces later. The crank breather connects to the intake so if there is oil in the intake it also can be from the breather system and not necessarily from turbo?

[newsh]

Yes, it can also cause smoke if the breather system is blocked or either of the PCV valves are not working properly.