For years, car makers have preached the gospel that engine oil needs to be changed every 3 months or 3 thousand miles, whichever comes first. This was because engine oil formulations from decades back degraded and broke down when left in the crankcase for longer than the prescribed interval. Heat, friction, and oil oxidation resulted in a particulate-filled and muddy mixture known as sludge. Sludge kills engines by gumming up oil passages and contaminating good oil. It can crystalize and harden from engine heat resulting in formations that cannot be removed except by an engine teardown. Sludge deposits can be prevented by using high quality engine oils, which will prolong engine life.
Modern vehicle engines operate at high heat and close tolerances. One of the reason for this is the Federal Emissions requirements that imposes fines and sanctions if minimum tailpipe emission controls are not met. One of the steps car makers have taken to meet these requirements is to increase combustion chamber temperatures with higher compression engines, running leaner fuel systems, adjusting ignition timing for optimum emissions, narrowing cooling system water jackets, and tightening engine oil tolerances. All this steps result in hotter running engines that emit less tailpipe emissions. However, these tighter tolerances put increased demands on engine lubricants and inferior formulations will allow the oil to break down more easily, thus promoting sludge buildup.
New research, development and cooperation between car makers and lubricant producing companies has resulted in improved engine lubricants that meet the requirements of today's higher performing engines and at the same time delay the onset of sludge buildup. This means that with modern high quality oils such as synthetics, oil changes can be extended to more than the traditional 3 months or 3,000 kilometers. In fact, the best synthetic oils used to flaunt 10,000 km changes but probably because of warranty and legal concerns, this extended change interval has ceased to be advertised.
Several manufacturers now boast of oil monitoring technologies to help extend oil change intervals. Oil monitoring systems look at crankcase temperatures, moisture, and combustion chamber events while the engine is in operation. The best systems can measure the serviceable life of a car's engine oil to within 10%. The result of the adoption of these technologies is that with normal vehicles use, many manufacturer had adopted a new recommended figure of 7,500 miles between oil changes. This presumes of course that the car owner will use the engine oil recommended by the car maker. To be on the safe side, DIY owners would be better off adopting a 5,000 mile oil change interval.
As with other technological breakthroughs, engine oils are much better nowadays and engines are much better protected, specially if synthetic oils are used. The owner must also remember to always use a good quality filter when having the engine oil changed. The filter is the storehouse for dirt in the engine and an old filter will allow dirt and grit to circulate within and on the engine bearing surfaces and virtually all metal mating surfaces. These will be damaged by the sandpaper action of circulating grit, resulting in wider oil tolerances, lowered oil pressure and ultimately premature engine failure.
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