Crankcase Ventilation Systems: Description

All 1965-67 engines are equipped either with "Positive" or "Closed Positive" crankcase ventilation systems. All 1968-74 engines are equipped with "Closed Positive" ventilation systems. Both "Positive" and "Closed Positive" ventilation systems utilize manifold vacuum to draw fumes and contaminating vapors into combustion chamber where they are burned. The "Positive" system consists of a vented oil filler cap, Positive Crankcase Ventilation Valve (PCV Valve), and a hose attached between PCV valve and intake manifold. The "Closed Positive" system consists of a non-vented oil filler cap, hose from carburetor air cleaner to rocker arm cover, a flame arrester, installed in hose between air cleaner and engine, and either a fixed orifice (1965), or a PCV valve (all other years) located in line from crankcase (rocker arm cover) to intake manifold.