The positive crankcase ventilation (PCV) valve is located on the intake manifold below the carburetor (if so equipped), or inline with (or on) the cylinder head cover. Routine periodic maintenance of this system basically involves inspection of the breather hose and replacement of the PCV valve.
When the engine is running, small amounts of combustion gases leak by the rotor seals and enter the rotor housings and oil pan. Since these gases are under pressure, they tend to escape into the atmosphere. If these gases were allowed to remain for any length of time, pressure would build up and possibly blow out an oil seal. They would also contaminate the engine oil and cause sludge to build up. If the gases were allowed to escape into the atmosphere, they would pollute the air, as they contain hydrocarbons. The crankcase emission control equipment recycles these gases back into the engine combustion chambers where they are reburned.
In the case of the rotary engine, the word crankcase is not quite correct, however, since the Mazda rotary engine has no crankcase in the usual sense of the term. As a result, rotary engines do not employ a conventional PCV valve. Instead, the "crankcase'' emission control equipment for 1979–80 models consists of a ventilation and check valve and its related hoses, which meter the flow of fuel and air vapors through the rotor housings and oil pan. When the engine is running, vacuum from the intake manifold opens the ventilation and check valve. This allows blow-by gases to flow out of the rotor housings and oil pan, and into the intake manifold where they mix with the air/fuel mixture to be burned in the combustion chambers. When the engine is not running, the ventilation valve is closed and blow-by gases are trapped inside the housings until the engine is started again. The ventilation and check valve also controls evaporative emissions, as explained later in this section.
NOTE: 1981–89 models do not contain a ventilation and check valve. In its place, a check and cut valve is used.