[QUOTE=Soo-Valley;1071552]I wondered about that too, oil pan vent. add/withdraw air from the sump to compensate for oil levels?
Yes, the vent will do that too. As the oil heats, cools and the engine pumps oil throughout the system the pan level will change.
But the main function is to strip oil from the blowby fumes which would otherwise spread all over the engine compartment making a big mess and sometimes foul the air in the cabins.
Newer engines have a fully functional crankcase venting system which leads those fumes back to the engine intake so they are burned in the combustion chambers.
Cleaner atmosphere and less smell and mess aboard.
My different engine, 1976, had a similar system for catching oil out of the fumes.
I altered that so the fumes are all lead back to the the engine intakes for the fumes to be burned. No more smell unless I forget to reconnect the hoses after doing some service work.
All engines, even brand new ones, produce blowby. THe question is how much.