Hello
most engines have a breather
On the move there is still a small part of the flue gas flowing through the segments. These ga zcontian the water vapor from the stubborn carburettor (especially when starting on gasoline and even more so on diesel direct injection (the guys who walk a 100% oil sometimes see their crankcase oil level increase)
Normally if the engine is in good condition, it is long enough to heat the engine oil to more than 100c
These contaminants, water and fuel that dilute the oil, evaporate and come out by the breather, the breather outlet for the engine is directly in the open air (on the aircraft if we return it by the carburetor there would have an additional risk of icing), most often it is to send behind the air filter, not to contaminate it and there is more depression behind the filter.
The breather must not be plugged, the pressure in the sump increases and forces the hot oil out through the seals and even break the seals of the vibrocamp, a slight depression in the sump removes many of the oil slides.
On many cars there is a PCV System (Positive Crankase Ventillation)
On the V6 or V8 engine There is an air intake caught in the back of the air filter that goes on the rocker cover of a row of cylinder and on the other rows of cylinder it goes into the intake manifold under the butterfly, with a small check valve (PCV valve), this way there is a forced ventilation of the housing ..
Andre
Some pose this accessory in place of the PCV valve which is a simple check valve