This is Alfa Romeo Giulietta installed oil separator. Disassembly shows the vent is guarded by a flat rubber circle pushed up by a spring. This rubber flab probably ensures the air only flows in. Other than that the separator is connected to the engine block for oil to drip, and has two hoses: one leading to the intake hose before turbo charger and the other probably to the crank case. Why would it have this vent in the cover?

oil separator


If the cover did not have a vent, then the membrane could only move if it compressed the air enclosed or caused a depression relative to atmospheric pressure which is not the effect the desingner / manufacturer was wanting...

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  • Sorry, I think I misnamed the thing. It is not really a membrane in the sense that it filters things, it is a large flat rubber sort of gasket that ensure the air can only come in not out. I don't think it is there to separate the oil. I'll edit the question. – luntain Oct 18 '18 at 17:50
  • A membrane does not have to be a filter... It may just be there to stop dirt ingress... – Solar Mike Oct 18 '18 at 17:52
  • Still don't understand your answer. The air is supposed to flow from the crank case through the separator into the intake. What is the vent for? – luntain Oct 18 '18 at 17:55

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