If the PCV (Positive Crankcase Ventilation isn’t working correctly, it can cause problems that range from poor idle quality and serious oil leaks to sludging and internal engine damage from oil contamination. Every piston engine no matter how well designed and assembled has a certain amount of blow-by past the rings, and if it can’t get out of the crankcase pressure will build up and water vapor, excess gasoline, and combustion contaminants will collect in and dilute the motor oil.