Nissan/Datsun 200SX/510/610/710/810/Maxima 1973-1984 Repair Guide

Crankcase Ventilation System



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Fig. Fig. 1 Fig. 1 PCV system schematic-L20B engine

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Fig. Fig. 2 PCV system schematic-Z20S engine

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Fig. Fig. 3 PCV system schematic-Z20E engine

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Fig. Fig. 4 PCV system schematic-L24 engine

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Fig. Fig. 5 PCV system schematic-LD28 engine

The crankcase emission control equipment consists of a positive crankcase ventilation valve (PCV), a closed or open oil filler cap and hoses to connect this equipment.

The crankcase emission control system on the diesel engine is basically the same as that which is on the gasoline engine. Its major difference is the crankcase emission control valve. Although its function is the same as the gasoline engine's PCV valve, it's shape and location are different.

When the engine is running, a small portion of the gases which are formed in the combustion chamber during combustion leak by the piston rings and enter the crankcase. Since these gases are under pressure they tend to escape from the crankcase and enter into the atmosphere. If these gases were allowed to remain in the crankcase for any length of time, they would contaminate the engine oil and cause sludge to build up. If the gases are allowed to escape into the atmosphere, they would pollute the air, as they contain unburned hydrocarbons. The crankcase emission control equipment recycles these gases back into the engine combustion chamber where they are burned.

Crankcase gases are recycled in the following manner: while the engine is running, clean filtered air is drawn into the crankcase through the air filter and then through a hose leading to the rocker cover. As the air passes through the crankcase it picks up the combustion gases and carries them out of the crankcase, up through the PCV valve and into the intake manifold. After they enter the intake manifold they are drawn into the combustion chamber and burned.

The most critical component in the system is the PCV valve. This vacuum controlled valve regulates the amount of gases which are recycled into the combustion changer. At low engine speeds the valve is partially closed, limiting the flow of gases into the intake manifold. As engine speed increases, the valve opens to admit greater quantities of the gases into the intake manifold. If the valve should become blocked or plugged, the gases will be prevented from escaping from the crankcase by the normal route. Since these gases are under pressure, they will find their own way out of the crankcase. This alternate route is usually a weak oil seal or gasket in the engine. As the gas escapes by the gasket it also creates an oil leak. Besides causing oil leaks, a clogged PCV valve also allows these gases to remain in the crankcase for an extended period of time, promoting the formation of sludge in the engine.


Check the PCV system hoses and connections, to see that there are no leaks. Then replace or tighten, as necessary.

Gasoline Engines

To check the valve, remove it and blow through both of its ends. When blowing from the side which goes toward the intake manifold, very little air should pass through it. When blowing from the crankcase (valve cover) side, air should pass through freely.

Replace the valve with a new one, if the valve fails to function as outlined.

Do not attempt to clean or adjust the valve. Replace it with a new one.

Diesel Engines

Remove the crankcase emission control valve and suck on the pipe that leads to the intake manifold. Air should flow freely. You should be able to hear the diaphragm in the valve click open while you are sucking. If the valve fails to function as detailed, replace it with a new one.


To remove the PCV valve, simply loosen the hose clamp and remove the valve from the manifold-to-crankcase hose and intake manifold. Install the PCV valve in the reverse order of removal.

Removal and installation procedures for the diesel crankcase emission control valve are detailed in .