How does the PCV valve affect oil consumption? I hope someone can explain this to me. Today, I replaced the PCV valve on my wife's Expedition 4.6L. For as long as we've owned the Expy, it has consumed oil, between 1.5 - 2.0 qt's of dino every 5k miles. FWIW, I just switched to Havoline full synthetic last week. After reading on BITOG that some folks have noticed their oil consumption dropping after installing a new PCV valve, I decided to give it a shot. The part was only $2.39 @AZ, so I figured "What the heck?" So, to re-state my question: How does the PCV valve affect oil consumption?