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Positive Crankcase Ventilation (PCV)
The PCV Valve

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PCV Valve Replacement: $30-$75 (Prices good for most domestic or import cars and light trucks)
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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 a device 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 manufacturers came up with POSITIVE CRANKCASE VENTILLATION or PCV. With this system, a vacuum is drawn on the engine crankcase from the intake manifold or carburetor 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.

PCV valve location

Usually the PCV valve is located in the engine valve cover. A vacuum hose from the PCV valve to the intake manifold. Some vehicles (mostly older ones) have the PCV elsewhere. Some place the valve in a tube or box on the side of the engine block. (this was where the old crankcase draft tube was located). Some have the valve screwed into the intake manifold with a hose going to the engine to suckn out the blowby gasses.

PCV inlet locations

The earliest PCV systems had a vented oil cap like the old draft tube motors. Most PCV inlets are now via a hose to the valve cover from the air cleaner. Sometimes the air cleaner has a separate filter for the PCV inlet hose. Engines with excessive blowby will sometimes fill the air cleaner with oil: there's more blowby than the PCV valve can handle so the blowby gas goes backwards into the air cleaner. A lot of cars have a broken PCV inlet hose: those cars are SUCKING DIRT AND DUST INTO THEIR ENGINE!!!

Here's some images of PCV valve locations


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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.


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Auto, Car, and Truck Article List

A
ABS: Anti-Lock Brake Systems
ADVANCE: Car ignition timing
ALTERNATORS and Car Battery
AUTOMATIC TRANSMISSIONS
B
BAD CAR DESIGNS
BATTERIES: Auto, Car or Truck
BELTS AND HOSES
BEARINGS
BODY AND BUMPER REPAIRS
BRAKE REPAIRS: Car or Truck
C
Car Washing and Care
CARBURETORS:Car & Truck
CHECK ENGINE LIGHT
CLEANING: Engine Cleaning
CLUTCH REPAIRS: Car & Truck
COMPRESSION: Car Engine
COMPUTER CAR CONTROLS
CV JOINT OR CV AXLES
D
DISTRIBUTORS (IGNITION)
E
ELECTRIC WIRING REPAIR
ENGINES: Car & Truck
ENGINE CLEANING
EXPANSION PLUGS
F
FREEZE PLUGS
FUEL AIR MIXTURE
FUEL INJECTION: Car & Truck
FUEL PUMPS: Car & Truck
G
GAGES AND "IDIOT LIGHTS"
GASKETS AND SEALS
GLASS: WINDOWS AND WINDSHIELDS
H
HEADS & HEAD GASKET
HOSES AND BELTS
I
"IDIOT LIGHTS" AND GAGES
IGNITION TIMING: Car & Truck
J
AUTO JACKS: lifting cars safely
K
L
LEAN "Car runs lean"
LIGHTS: WARNING OR "IDIOT LIGHTS"
Limp Home Mode
M
MIL Light
MANUAL TRANSMISSIONS
N
NO START: Car Won't Start
O
OIL CHANGES
OIL: What's right for your car?
OIL LIGHT ON OR GAGE LOW
P
PCV Valve
Q
R
RADIATORS: Car and Truck
RICH: Car runs rich
S
SEALS AND GASKETS
SERVICE ENGINE SOON LIGHT
SPARK PLUGS
STARTERS: Auto, Truck
T
THERMOSTATS
TIMING: IGNITION TIMING
TIMING BELT & TIMING CHAIN
TIRE REPAIR
TRANSMISSIONS: AUTOMATIC
TRANSMISSIONS: MANUAL
U
V
VACUUM ADVANCE
WARNING LIGHTS OR "IDIOT LIGHTS"
Car Washing and Care
W
WATER PUMP REPAIR
WINDOWS AND WINDSHIELDS
WIRING REPAIR
X
Y
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