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Old 05-19-2016, 08:44 PM
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X5only X5only is offline
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Originally Posted by stiubhartach View Post
I would be very surprised if a valve stem seals were leaking enough under vacuum to show visible smoke, but not leaking while the engine is off. Did you try pouring oil into the return passage and watching flow down? That's a hard place to clean.

This I some basics on valve seals:

Automotive Valve Seals: Symptoms Smoke at Startup

This is great post on the CCV system in the n62. Specifically post 18 has some more tests.
Trust me, I did make sure there was no obstruction to oil flow. I just read a post where another DIY whose smoking issue at idle was NOT as a result of valve stem seals leak but as a result of vacuum leak! It's a very interesting thread and concurs with you.

He, like you, does not believe that smoking only at idle is a valve stem seal leak. Looks like the mechanics have been taking us for a ride or what?

I just got some pcs seals for the passenger side as that is leaking and, guess what, only the passenger side exhaust leaks.

I will report tomorrow if that fixes anything.

"A.) Immediately after a cold startup - the first startup after a prolonged period of the engine being off, like sitting in your garage over night?
If so, valve stem seals could be your issue; but I believe this to be a limited failure only seen in the early 745i.

B.) Or, like mine, does the smoke appear as an embarrassing cloud of shame - typically after accelerating from prolonged idling, like sitting at a really long stop light or stop and go traffic...?

Cause of A.)Valve Stem seals only leak down, meaning they have to sit for a long time and be cold (small) enough for oil to slowly drip past them; theoretically, it could deteriorate to the point where would leak all of the time, but you’d see the smoke issue as a constant factor, rather than just when the engine is warm. When valve stem seals get warm, they expand. The expansion would reseal the path the oil was leaking through until the seal cooled to the point where it was small enough for oil to seep past. This is why failing
valve stem seals can cause smoking at startup - oil has dripped past, collected in your cylinder, and then gets burned off the next time the car starts….and the smoking stops when it gets warm…only to return the next time your car has been sitting and is cold.

Cause of B.) is caused, essentially, by a vacuum leak that prevents the PRVs from sealing...drawing oil into your intake.
'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.

Last edited by X5only; 05-19-2016 at 08:50 PM.
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