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What is a PCV valve and what does it do?

What is PCV

Many cars come fitted with a PCV (positive crankcase ventilation) valve as part of the breather system – especially those systems with a pipe connecting the breather to the inlet manifold.

At low engine speeds, this will actually help draw any blow-by gases out of the crankcase and recycle them through the inlet – meaning no oily deposits are dumped on the road.

But if the engine was to backfire the one-way PCV valve closes to prevent the breather system being subjected to the high temperatures of a backfire.

The PCV is also used in turbocharged engines, where a pressurized inlet manifold (under boost conditions) would mean blowing boost directly into the crankcase if a one-way valve were not fitted

How does a PCV work