AC Delco, Motorcraft and Fleetguard Cummins Filtration's crankcase ventilation systems are made to meet or exceed the original products using patented technologies to control oil drip and crankcase emissions in diesel engine applications. The open crankcase ventilation systems provide superior aerosol filtering of crankcase emissions, commonly known as blow-by. Blow-by is the result of high pressure gases and oils escaping around piston rings and venting to the atmosphere. This crankcase oily mist attracts dust and airborne particles, resulting in an accumulation of contaminants, both on the engine and on the surface beneath it. PCV Valves reduce this condition and the clean-up required in the engine compartment, as well as unsightly oil drips on highways, bodies of water, parking lots, crops, garage floors and driveways.