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.
Description & Operation
Crankcase ventilation systems prevent hydrocarbons from entering the atmosphere by routing vapors from the crankcase, through a vacuum-controlled ventilating valve (PCV valve), into the intake manifold. In the intake manifold the vapors are burned in the combustion process. See Fig 1 .
The valve is held closed by spring pressure when engine is not running. This prevents hydrocarbon fumes from collecting in intake manifold, which could result in hard starting.
When engine is started, manifold vacuum pulls valve open against spring pressure. As long as there is engine vacuum, the valve floats, permitting crankcase fumes to enter intake manifold. If the engine backfires, the ventilator valve will close to prevent ignition of fumes in crankcase.
During certain engine operations, more blow-by is created than ventilator valve can handle. Excess blow-by is returned to air cleaner and carburetor through rocker arm cover and breather assembly. It is then burned in the combustion chamber. The breather assembly acts as separator to keep oil from being drawn into air cleaner during this operation.
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.