Most people know that engine oil provides protection against friction by creating a thin barrier of oil between the moving parts. But engine oil does more than reduce friction and prevent wear and damage. Did you know that oil also helps keep your engine clean? Dust and dirt that may have slipped by the air filter, along with contaminants produced during the combustion process are captured and retained by the engine oil. The oil filter removes the larger particles as the oil passes through it, but the oil still retains and continues to collect contaminants during its useful life. This is why new engine oil is light in color and old engine oil is very dark. By not changing the oil on your GMC at the scheduled intervals, the free contaminants in your engine could cause premature wear to engine components.In addition to lubricating and removing dirt, engine oil also helps keep the engine cool. As oil circulates through the engine, it rises in temperature and carries that heat to the oil pan which is exposed to constant air flow when your vehicle is in motion, which helps dissipate the heat away from the engine. Some heavy duty vehicles may use an oil cooler, mounted behind the front grill near the radiator to further help reduce the heat carried by engine oil.