No matter how meticulous you are about oil changes there are areas inside every engine where oil doesn’t circulate well. The oil sits in depressions in metal castings of the engine where it slowly becomes thick and gooey from heat. Over time this forms chunks of sludge that move about inside the engine. As these chunks find their way to the oil pan they’re sucked into the oil pump pickup screen where they eventually restrict the amount of oil that can circulate for lubrication. Net result — shortened engine life.