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Positive Crankcase Ventilation (PCV)

The PCV valve, commonly located in the valve cover with a hose connecting it to the intake manifold, reduces HC and CO (blow-by crankcase emissions). Blow-by is unburned fuel and water vapor that gets past the cylinders and into the crankcase when the engine runs. Vacuum pressure in the PCV system sends blow-by through the PCV valve into the intake air to be burned during combustion. Reducing unburned fuel and water vapor provides other benefits. Water can turn oil into sludge, while unburned fuel can dilute oil. If not handled correctly, blow-by can cause corrosion and increase engine wear.