عبور روغن از کاسه‌نمدهای فرسوده توربوشارژر

Oil passing the turbocharger's shaft seals into the intake or exhaust. A turbocharger is oil-fed under pressure and sealed by ring seals rather than lip seals, so some carryover is normal and excessive carryover means wear — or a drain that cannot cope.

On the compressor side it coats everything downstream: the intercooler fills, the ducting films with oil, the airflow sensor is contaminated, and the intake valves and filter foul. Oil in the intercooler is the confirming finding and is the strongest evidence of turbocharger seal wear available without dismantling.

Check the drain before condemning the turbocharger. A blocked or kinked oil return, or a crankcase under pressure from a failed breather, backs oil up past seals that are in perfect condition — so this is frequently a symptom of something else. A restricted return produces the same oil carryover as worn seals, and fitting a new turbocharger without clearing it destroys that one too.