GM Full Size Vans 1967-1986 Repair Guide

Crankcase Ventilation System



See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Diesel engine emissions components

A Crankcase Depression Regulator Valve (CDRV) is used to regulate (meter) the flow of crankcase gases back into the engine to be burned. The CDRV is designed to limit vacuum in the crankcase as the gases are drawn from the valve covers through the CDRV and into the intake manifold (air crossover).

Fresh air enters the engine through the combination filter, check valve and oil fill cap. The fresh air mixes with blow-by gases and enters both valve covers. The gases pass through a filter installed on the valve covers and are drawn into connecting tubing.

Intake manifold vacuum acts against a spring loaded diaphragm to control the flow of crankcase gases. Higher intake vacuum levels pull the diaphragm closer to the top of the outlet tube. This reduces the amount of gases being drawn from the crankcase and decreases the vacuum level in the crankcase. As the intake vacuum decreases, the spring pushes the diaphragm away from the top of the outlet tube allowing more gases to flow to the intake manifold.

Do not allow any solvent to come in contact with the diaphragm of the Crankcase Depression Regulator Valve. The diaphragm will fail.


Do not attempt to test the valve. If you suspect problems with the system, clean the filter and vent pipes with solvent. Be sure to dry the components before installing them.


See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the crankcase ventilation system used on diesel engines

The components of this system can be removed by disconnecting the hoses and pulling the component from its mounting grommet. Be careful not to damage the grommet; replace if necessary.