Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.