When your engine is running, air pressure builds up inside the crankcase, the compartment where the crankshaft and engine oil is located. This pressure is caused by exhaust gases produced during combustion that leaks past the pistons and into the crankcase. If left unchecked, the exhaust can contaminate the engine oil and create sludge. Excess crankcase pressure can also lead to engine leaks.
The PCV valve is a one-way valve that allows the gasses inside the crankcase to be rerouted to the engine intake where they are able to be drawn into the engine to be burned. In the process, the vapors are prevented from entering the atmosphere. For this reason, the PCV valve is often considered to be part of the emission control system.
Made up of a small cylinder that is inserted into the intake manifold, valve cover, or engine block, the PCV valve connects to the crankcase by way of a tube or hose. On some vehicles, the valve has an internal weight that “rattles” during operation. This sound is a sign of normal operation, one that some technicians pay attention to as part of a diagnostic procedure.
If the PCV valve is not working properly, the oil inside your engine will eventually collect contaminants and moisture. When the oil breaks down, a loss of viscosity and engine sludge are the results. Engine leaks can also develop from the excessive pressure inside your engine. A faulty PCV valve can lead to any of the following symptoms:
The procedure to replace a PCV valve is not altogether complex. To perform the service, a technician will follow these general steps: