Originally Posted by metroplex
I understand that, I meant the part about the valve deposits forming on GTDI intake valves caused by this. If you browse the EcoBoost forums, everyone is pushing oil separators and catch cans hard - the same goes for other brands of GTDI engines. The assumption was the deposits were formed primarily by oil from the PCV system, no one ever mentioned the valve stem seals. I know from experience that the factory PCV oil separators on my EcoBoost engines have been very effective. The only thing they catch are volatile vapors that coalesce and burn very readily. Almost all the oil I found in the intake tract came from the turbochargers.
Because they're uninformed. Leaky stem seals contributing to consumption, piston deposits and IVD's is a bona fide "thing". And so is recirculated oil vapour via the PCV.
A lot of times the valve guide over time develops play which in turn accelerates wear on the seals. Sometimes it's lack of adequate lubrication or sometimes the seals just plain wear out..they do have a finite lifespan.