Chrysler Full-Size Vans 1989-1998 Repair Guide

Crankcase Ventilation System



See Figures 1, 2, 3 and 4

When the engine is running, a small portion of the gases which are formed in the combustion chamber 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 are 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 intake air filter and then through a hose leading to the oil filler cap or the valve 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 are burned.

The most critical component of the system is the PCV valve. This vacuum-controlled valve regulates the amount of gases which are recycled into the combustion chamber. 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 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.

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Fig. Fig. 1: Schematic of a common PCV system

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Fig. Fig. 2: PCV valve position with no vapor flow-engine off or backfiring

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Fig. Fig. 3: PCV valve position with minimal vapor flow-high intake manifold vacuum

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Fig. Fig. 4: PCV valve position with maximum vapor flow-moderate intake manifold vacuum


See Figures 5, 6 and 7

  1. Remove the engine cover.
  3. With the engine running, pull the PCV valve and hose from the valve rocker cover rubber grommet. A hissing noise should be heard as air passes through the valve and a strong vacuum should be felt when you place a finger over the valve inlet if the valve is working properly.
  5. While you have your finger over the PCV valve inlet, check for vacuum leaks in the hose and at the connections.
  7. When the PCV valve is removed from the engine, a metallic clicking noise should be heard when it is shaken. This indicates that the metal check ball inside the valve is still free and is not gummed up. If not operating properly, replace the valve.
  9. If no vacuum is felt when the PCV valve is removed from the engine, remove the valve from the hose and check the vacuum supply in the hose.
  11. Check the condition of the breather element. Clean or replace as necessary.
  13. Check the breather hose for restrictions.
  15. Check the intake manifold fittings for sludge buildup, this can reduce the flow of the system.
  17. Install the engine cover.

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Fig. Fig. 5: PCV system components-V6 engine

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Fig. Fig. 6: Crankcase breather filter

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Fig. Fig. 7: The PCV valve fits into a grommet on the valve cover; replace the grommet if it leaks


Refer to General Information & Maintenance for removal and installation of the PCV valve and breather element.