The PCV valve is a little, inexpensive part that does a big job for our environment. PCV stands for Positive Crankcase Ventilation. The crankcase is the bottom area of the engine that holds the oil. When the engine's running, fuel is burned to generate power. Most of the exhaust from combustion goes out through the exhaust system. But some exhaust blows by the pistons and goes into the lower engine, or crankcase.
These hot gases are about 70 percent unburned fuel. This can dilute and contaminate the oil, leading to damaging engine oil sludge. It can also cause engine corrosion. At high speeds, the pressure can build up to the point that gaskets and seals start to leak. Over time, the vented gases will gum up the PCV valve and it won't work well. That can lead to oil leaks, excessive oil consumption and reduced fuel economy.
Fortunately, it's very easy to test the PCV valve, and it's quick and inexpensive to replace. Even so, it's often overlooked because many don't know about it. If this is the first time you've heard of a PCV valve, you might be in line for a replacement.