With your engine fully warmed up (maybe after a run on the highway) and at idle, loosen your oil filler cap and see if there is positive pressure behind it. Also you may find some pressure or splashback at your dipstick. If you find these problems the system as you describe it is not working, probably clogged (or else your engine is in very bad condition with severe blowby - seems unlikely). If the system is working ok the pressure will be more or less zero (not much vacuum if any).

If bad do as Klaus says.