Crankcase Depression Regulator

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The Crankcase Depression Regulator (CDR) valve, located on right-side valve cover, is used on all diesel engines. Valve prevents crankcase pressure from accumulating during idle by regulating (metering) crankcase pressure back into the engine. Intake manifold vacuum (only slight vacuum is present) acts against a spring-loaded diaphragm to control flow of crankcase gases. Higher intake manifold vacuum levels pull diaphragm closer to the top of the outlet tube, reducing amount of gases drawn from crankcase. As intake manifold vacuum drops, spring pressure pushes diaphragm away from top of outlet, allowing more gases to flow from crankcase into intake manifold.

Optimum pressure in crankcase is one in. H2O (as measured with a manometer) at idle to 3-4 in. H2O at full load. Too little vacuum causes oil leaks; too much vacuum pulls oil into the air crossover.