Aside from Performance Specifications and any other off-topic, I think these comments are worth consideration. From: Chapter 17 SYNTHETIC LUBRICANT BASE STOCK PROCESSES AND PRODUCTS Margaret M. Wu(a) (b) and T. Rig Forbus(c) (a) ExxonMobil Research & Engineering Co. Annandale, NJ 08801 (b) ExxonMobil Chemical Co. Synthetic Division, Edison , NJ 08818 (c) The Valvoline Co. of Ashland, Inc., Lexington, KY 40512
Comment. The statement in Bolded-Italics is what has concerned those in the industry. I.E., if Group II+ (especially) can be considered a synthetic base oil, then could not a Group II or even a highly refined Group I, or I+, be considered as a synthetic as well? Stated differently, how far do we go in considering what is a synthetic? Do we define it according to the generally accepted chemical definition stated below, or do we let Marketing interests define it? And how much chemical "transformation" does it take to consider it a synthetic? Some would say Marketing interests have been allowed to define it ex post facto, [from the Latin, "from a thing done afterward."]
...Many U.S. base oil manufacturers and formulators include some Group II+ and Group III base stocks as synthetic as their manufacturing process includes varying degrees of chemical transformation. These base stocks are usually produced by hydroprocessing or hydroisomerization, which is typically part of a refining process...(J. Synth. Lubr., 2002, 18-4, Publisher‘s Note).
Synthetic lubricants differ from conventional lubricants in the type of components used in the formulation. The major component in a synthetic lubricant is the synthetic base stock. Synthetic base stocks are produced from carefully-chosen and well-defined chemical compounds and by specific chemical reactions. The final base stocks are designed to have optimized properties and significantly improved performance features meeting specific equipment demands. The most commonly optimized properties are: - Viscosity Index (VI). VI is a number used to gauge an oil‘s viscosity change as a function of temperature. Higher VI indicates less viscosity change as oil temperature changes - a more desirable property. Conventional 5 cSt mineral oils generally have VIs in the range of 85 to 110. Most synthetic base stocks have VI greater than 120. Pour point and low temperature viscosities. Many synthetic base stocks have low pour points, -30 to -70°C, and superior low-temperature viscosities. Combination of low pour and superior low-temperature viscosity ensures oil flow to critical engine parts during cold starting, thus, offering better lubrication and protection. Conventional mineral oils typically have pour points in the range of 0 to -20°C. Below these temperatures, wax crystallization and oil gelation can occur, which prevent the flow of lubricant to critical machine parts. - Thermal/oxidative stability. When oil oxidation occurs during service, oil viscosity and acid content increase dramatically, possibly corroding metal parts, generating sludge and reducing efficiency. These changes can also exacerbate wear by preventing adequate oil flow to critical parts. Although oil oxidation can be controlled by adding antioxidants, in long term service and after the depletion of antioxidant, the intrinsic oxidative stability of a base stock is an important factor in preventing oil degradation and ensuring proper lubrication. Many synthetic base stocks are designed to have improved thermal oxidative stability, to respond well to antioxidants and to resist aging processes better than mineral oil. - Volatility. Synthetic base stocks can be made to minimize oil volatility. For example, polyol esters have very low volatility because of their narrow molecular weight distribution, high polarity and thermal stability. Similarly, careful selection and processing of raw materials can influence the finished properties of polyalphaolefins (PAO) base stocks. - Other properties, including friction coefficient, traction coefficient, biodegradability, resistance to radiation, etc. can be optimized for synthetic base stocks as required for their intended applications...