Type 1/1600, 2/1600, 2/1700, 2/1800 (Carbureted)
The crankcase is vented by a hose running from the crankcase breather to the air cleaner. In some cases the hose is attached to the air inlet for the air cleaner. No PCV valve is used. No regular service is required.
Type 2/1800, 3/1600, 4/1700, 4/1800 (Fuel Injected)
Air is drawn in from the air cleaner to the cylinder head covers and pushrod tubes where it passes into the crankcase. From there, blow-by fumes then pass into the crankcase breather where they are drawn into the intake air distributor. On some models a PCV valve is used to control the flow of crankcase fumes. These systems usually need no maintenance other than keeping the hoses clear and all connections tight.
Many VW engines do not use a conventional PCV valve because engine design limits crankcase pressure pulsing and allows almost no oil vapor to go into the PCV system.