I am looking for theory and operation on fixed orifice PCV designs. My GM service manual provides little information on it. Interested in learning about the pro's and con's of this type of crankcase ventilation. My 2012 GM Ecotec Gen II 2.4l has a fixed orifice in the intake manifold/cylinder hear flange and fresh air feed from the air plenum with a basic separator. These engines are prone carbon build-up in the orifice and when the separator fills up and freezes, crankcase pressures rise and blow the rear seal. I am aware of the TSB on this problem. A vented breather cap with a check ball is not an option and just a bandaid. I assume the fresh air side also serves to evacuate the crankcase at speeds and higher loads, as the fixed orifice will only flow so much volume at a given vacuum. I am seeing 20" of Hg at idle and drops to 5" and even less than 1" at moderate loads at highway speeds. The fixed orifice obviously will not remove the blow-by at the rate necessary so I assume the air flow through the air plenum makes up the difference in theory. At these speeds and loads, during cold, high humidity (snow and rain) I see large amounts of moisture, oil and blow-by in the fresh air separator and the oil fill cap is heavily coated. During the same weather conditions, driving in the city, with much higher vacuum readings, the crankcase and separator stays clear, even in short trips, where the engine does not fully reach operating temps. I have been searching the internet and forums for more detailed information on fixed orifice PCV theory. I see that it is favored over traditional variable PCV valve designs when it comes to ECU fuel management and reduction in oil consumption. Any knowledge shared and links to more details would be appreciated.