Have you ever wondered what happens when you don't change your oil at the scheduled intervals? The answer is sludge, and LOTS of it. As oil ages in your engine it breaks down . The properties change and soon enough is doesn't lubricate any more. Whats worse is it will plug necessary passages that need to direct oil to critical components and cause premature engine wear and ultimately failure. So do yourself a favor and change your oil regularly. As a matter of fact, replace your fuel filter while your at it. Spend a little, to save a lot.