All 1968 and newer passenger cars and 1968 through 1978 light-duty trucks with a manufacturer's GVW of 6,000 pounds or less, and 1979 and newer light-duty trucks with a manufacturer's GVW of 8,500 pounds or less are equipped with a crankcase ventilation system. Early model vehicles may be equipped with an open crankcase ventilation system where air is drawn in through the oil filler tube. Later model vehicles are equipped with a closed crankcase ventilation system where air is drawn in through the carburetor air cleaner. On this type system, the oil filler cap is sealed.