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Because synthetic oils are more durable, they last longer and require less-frequent oil changes. Conventional oil requires oil changes every 3,000-5,000 miles, while certain synthetic oils, such as Mobil 1 Annual Protection and Castrol Edge Extended Performance oil can last up to 20,000 miles. AMSOIL Signature Series Synthetic Motor Oil is guaranteed for up to 25,000 miles or one year. So, you can see the shift to using synthetic oil provides a huge extension in time between oil changes.

The American Petroleum Institute (API) places different types of oil lubricants into categories based on their properties. Group I and Group II are comprised of base oils that are derived from crude oils. Group III oils are also derived from crude oils but are highly refined and are legally allowed to be considered “synthetic”, as ruled by the U.S. court system on behalf of Group III manufacturers. Group IV and Group V are reserved for synthetic base oils, with Group IV being entirely made of polyalphaolefin (PAO) oils. PAOs are synthesised by polymerising an alphaolefin molecule. Other synthetic base oils are placed in Group V, which is essentially any synthetic oil that is not made of polyalphaolefins.

Synthetic oils are certainly no stranger to controversy, having instigated countless debates and confusion spanning virtually every automotive forum, and this polemic is often not without merit. Legally, as we just learned, the term “synthetic” has a very broad definition. While some manufacturers prefer the word “synthetic” to apply only to chemically engineered oils, drawing a more pronounced distinction between synthetic and conventional oils, that is not how the rating system is used. Derivation notwithstanding, Group III through V oils have advanced properties and have withstood additional chemical processes that render them significantly different in terms of quality from Group I and II oils. By itself, the group rating is insufficient information to discern if a specific oil is superior to another. Each group has individual advantages and disadvantages.

Over time, conventional base oils break down when exposed to the shearing action of an engine, extreme engine temperatures and contaminants. Conventional oils are less shear-stable, which means they break down and lose viscosity easier. Conventional oils also are less resistant to oxidation, meaning the oil can thicken over time when exposed to heat. The combination of these performance deficiencies makes


controlling the viscosity of conventional oil over the course of the service interval very difficult. Ideally, oil viscosity at the end of the service interval should match the viscosity of new, unused oil. Maintaining viscosity over the service interval is of utmost importance to reducing engine wear. Synthetic oil, on the other hand, naturally provides improved viscosity control. Synthetic base oils are naturally shear-stable and resistant to oxidation, making viscosity control much easier.

This is significant since engineers design engines to work best using an oil that flows at a specific rate, depending on engine temperature and rpm. As the oil ages, changes in viscosity alter the oil’s flow characteristics, and this changes how well the oil protects against wear. Therefore, maintaining viscosity over the course of the service interval is very important.

There are many reasons automotive companies have adopted synthetic oils. They provide improved wear protection, corrosion resistance, viscosity control, engine cleanliness and fuel economy. It took decades for motorists to embrace synthetics. The acceleration of synthetics in the coming years will be far more rapid than in the past. If you haven’t considered changing to synthetics, now’s the time.

Dr. Raj Shah has a Ph. D in chemical engineering from Penn State University and is an elected Fellow at STLE, NLGI, AIC, INSTMC, RSC and EI. The science council has conferred upon him the status of a chartered scientist, he is a charted petroleum engineer from the Energy institute, and a chartered chemical engineer from IChemE. Currently he is the director at Koehler instrument company, in Long island, NY. He can be reached at

Mark Nyholm has a bachelors degree in mechanical engineering from Michigan Technological University and is currently the Technical Manager for Heavy Duty oils and Mechanical R&D at AMSOIL, Superior, WI


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