Oil is used in an engine to lubricate its moving parts. As the oil circulates in the engine it picks up rust, metal shavings and dirt. The oil filter removes this debris from the oil to prevent engine wear caused by these foreign particles, keeping the oil in the engine clean. What happens if you dont regularly replace your oil filter? The oil filter becomes clogged with dirt and oil flow is restricted. A filter relief valve is built into the filtering system, located either in the engine, oil filter base (attached to the engine) or in the filter itself. Under normal operating conditions this valve is closed. However, whenever the filter becomes clogged with dirt and restrictive to oil flow, the valve will open and supply oil directly to the engine. The oil carrying dirt, rust and metal shavings will enter the engine, potentially causing irreparable damage.