Why do you need to replace the oil filter with every oil change?

Modern engine oils do more than lubricate-they help remove harmful engine deposits and contaminants as you drive. The oil suspends these contaminants and carries them to the oil filter where they are trapped and held. Eventually, the oil filter becomes so saturated with these contaminants that its filtering capability is significantly reduced or made totally ineffective. If the oil filter is not replaced at the recommended intervals, unfiltered oil will continue to flow through the engine and cause excessive wear, which will reduce performance and ultimately shorten the life of the engine.