To avoid engine-killing sludge buildup, you must pick the right oil-change schedule – either normal or severe. This will involve an honest evaluation of your driving habits. Highway driving is easy on cars. Short trips and traffic are extremely hard on cars. Whichever you do more often determines how many miles or months you can go between changes. It is your decision, but be realistic. If there’s doubt, use the severe service schedule.
Second to changing oil is properly maintaining your cooling system. To be safe, check the coolant, and all vehicle fluids, according to the shortest time or distance recommended, not the longest. Coolant, even extended-life variants, should be tested for conditions every six months and coolant levels should be checked monthly. Proper testing may prompt you to flush and refill long before the extended-life interval has been achieved. A word of warning: never allow coolant to stay in the radiator until it changes color, because that change indicates rust, and rust is essentially dissolved engine.