The oil filter is a part of the oiling system on an internal combustion engine. The filter takes dirty oil and removes particulates and metal flakes from the oil. The cleaned oil is recirculated through the engine after leaving the filter. oil filters should be replaced along with the oil as the new oil can pick up the contaminants trapped in old oil filter and re-circulate them to engine's moving parts. Frequent oil and filter changes are an effective and economic way to increase engine life.