2L Oil Catch Can2L Chrome Finished Alloy Oil Catch Can, Most modern vehicles use a Positive Crankcase Ventilation system which is designed to regulate and remove fumes from the engine crankcase, and to alleviate crankcase pressure which could cause oil leaks or seal damage. It's a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine. Usually, the system is designed to recirculate the vented pressure back into the air