During the power stroke of an engine in operation, some by-products of combustion leak past the piston rings and end up in the crankcase. If the contaminants are left in the engine oil, the lubricity is diminished and sludge and acids form. Condensation will then develop, and pressure will build.

For this reason, every engine has a means to ventilate the crankcase. If the oil pan wasn’t ventilated properly, then the engine life would be dramatically reduced.

Gasoline engines do this by means of a positive crankcase ventilation (PCV) system. This is a valve that is operated by engine vacuum. 

The PCV is a highly engineered part that has a specific flow rate and response to the vacuum signal it receives. It consists of an outer shell with a vacuum fitting along with an internal spring, pintle, and seat for it to close against. 

The valve installed in the engine at the factory is exactly matched to the flow rate, but it’s designed to not skew the mixture delivery from the carburetor or fuel-injection system. The signal that operates the PCV can be thought of as a controlled vacuum leak. 

Many aftermarket PCVs have one internal design; only the exterior is changed to physically fit the engine. To your eyes, the valve looks the same and fits well, but it is all wrong inside. This can then result in several problems.

Also, a PCV with the wrong flow rate can result in many rear main seals being replaced and carburetors rebuilt to no avail. Many times, owners just give up and write it off to the engine being old.

If it’s still offered, always use a factory-replacement PCV. It is certainly worth the few extra dollars. If the original factory part is not offered, then opt for a high-quality, American-made replacement from a known company. 

To determine if the replacement PCV is impacting the carburetor, remove and plug the vacuum line, and leave the valve out so the engine can breathe. The PVC is the problem if the gas-air mixture is skewed. 

M/E Wagner makes an adjustable PCV for $120 that can be calibrated to almost any application to solve this concern. 

By the way, shaking the PVC and hearing it rattle only proves that your arm and ears work! This action gives absolutely no indication of its flow and transition abilities. 

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