We can not stress enough how important it is to change your engine oil regularly. Over time oil breaks down and causes sludge. If the sludge build up gets excessive, engine damage will occur. Changing oil every 3000 miles is the best way to avoid sludge. Also using the correct weight motor oil is very important. Todays engines are built with smaller tolerances and oil passages. they use lighter viscosity oil in order to keep the oil flowing through the engine properly. Always make sure the correct viscosity oil is used when having your oil changed. 5w30, 5w20 and even 0w20 oils are quite common on most late model vehicles.