Positive crankcase ventilation (PCV) is now standard equipment on all new automobiles. This paper presents data on the influence of oil quality and drain frequency on the maintenance requirements of these devices. The result of system malfunction on engine deposit formation in the field is also discussed. Engine age, oil age, and oil quality are shown to be important factors affecting the time to PCV valve malfunction. A multicylinder laboratory engine test has been used successfully to predict the valve plugging tendencies of lubricants in field service.