WHAT IS A PCV VALVE?

Although the PCV valve is considered an emission control, they have been around long before emission controls came around in the mid to late 1960's. The first PCV valves showed up in the late 1950's / early 1960's.

To understand the PCV system, you first need to understand some basic engine principles. When the fuel/air mixture is compressed and burned in the cylinder, high pressures are built up in the cylinder. Some of this pressure leaks past the piston rings, even on a new engine. These gasses which leak past the piston rings are called Blowby Gasses, because they "blow by" the piston rings. These gasses end up in the crankcase. They've got to go somewhere, or all the gaskets and seals in the engine would blow out from the pressure!

HISTORY OF CRANKCASE VENTILATION

Engines used to have adevice called a "crankcase draft tube" to vent the crankcase. It was just a tube hanging off the side of the engine. As the vehicle went down the road, air passed over the end of the tube, creating a vacuum. The blowby gas exited the engine through this tube. An oil cap was used with a filter element in it: clean air would enter through this at the valve cover.

This system was simple and worked very well. The problem came when America moved to the suburbs in the late 50's. Those draft tubes always had a little drop of oil on them. Those little drops put stains on all those clean, white driveways and carports, even when the car was brand new!

PCV TO THE RESCUE!!!

To save the driveways of America, auto makers came up with POSITIVE CRANKCASE VENTILLATION or PCV. With this system, a vacuum is drawn on the engine crankcase from the intake manifold or carburator base. A valve is put in this line which closes under low vacuum. This enables the engine to have no PCV action when starting, or at low vacuum. When the engine runs, air is sucked through the pcv valve, taking the blowby gasses into the intake manifold, where they are burned. To prevent a vacuum from developing in the crankcase, fresh air is admitted through a special filter. This filter was originally the same "filter cap" that the draft tube used. Later engines have the filter on the air cleaner, usually with a tube leading to one valve cover.

HOW THEY FAIL

A clogged PCV vacuum system can cause oil leakage. Blowby pressure builds up in the crankcase: the oil seals blow out. Often the air cleaner will fill with oil: the pressure goes backwards through the inlet filter.

A dirty PCV valve can not shut fully when starting, making a hard start problem.

A clogged PCV inlet filter or hose can cause a vacuum to build in the crankcase, which can also destroy oil seals.

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We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry!

Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.