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. Oil filter becomes saturated with these contaminants and their filtering capability is significantly reduced. If the oil filter is not replaced at the recommended intervals, contaminated oil will continue to flow through the engine and cause excessive wear, which will reduce performance and ultimately shorten the life of the engine.