Every car has a crankcase ventilation system that should suppress oil from making it into the intake ports and combustion chamber.
A good functioning system will separate oil from the atmosphere and return it to the oil pan (or collect it in a catch can) while allowing the leftover vapours to burn in the combustion chamber or recirculate through the system.
This has always been known as a Positive Crankcase Ventilation system (PCV) but there are other names for it such as oil separator, crankcase vent (CCV), and cyclonic separator.
Failures in the system will allow raw oil to enter the intake and eventually into the engine itself which can have disastrous effects on engine performance and longevity.
As emissions regulations have become more stringent, the PCV systems also become more complex and prone to potential failure.
The CCV is intertwined with other systems so any problem can result in rough running, loss of power, higher oil consumption, misfiring, stalling, or other annoying issues.
There is no replacement interval for these so we recommend inspecting your crankcase vent system as part of your regular maintenance routines.
Symptoms of a bad crankcase vent are: whitish or yellowish film on the underside of the oil cap, whistling/squealing noises (not caused by a belt), suction on the oil cap that makes it hard to unscrew, large amounts of white smoke from the exhaust, and excessive oil consumption.