ACDelco PF46F FLEET PK. OIL FILTER Excellent filter capacity, enhanced efficiency, consistent flow management and high durability make this oil filter the best you'll find Tight seals prevent unfiltered oil from entering your engine Consistent, dependable oil filtration throughout the filter Antidrain back valves retain oil in the filter for quicker engine lubrication during start-up By-pass valves help keep the engine from becoming oil-starved during cold weather starts or if total filter blockage exists