All engines use a sealed Crankcase Ventilation (CV) system that does not allow fresh air into the crankcase. This means the crankcase is under vacuum at all times and any leak in the system is a vacuum leak. It is important to make sure all hoses are in good condition and the dipstick O-rings are in good condition and the dipstick is firmly sealed in the tube. If the dipstick tube is not firmly seated, a vacuum leak will occur, which may cause engine oil to be drawn into the intake manifold.
The crankcase ventilation system draws the crankcase vapors through a connection on the valve cover. The vapors are drawn into the intake air stream and burned with the air and fuel mixture. This reduces the emission of hydrocarbons into the atmosphere.