PERFORMANCE Advantages The technical advantages of synthetic motor oils include: Measurably better low- and high-temperature viscosity performance at service temperature extremes Better chemical & shear stability Decreased evaporative loss Resistance to oxidation, thermal breakdown and oil sludge problems Extended drain intervals with the environmental benefit of less oil waste. Improved fuel economy in certain engine configurations. Better lubrication during extreme cold weather starts Longer engine life Superior protection against "ash" and other deposit formation in engine hot spots (in particular in turbochargers and superchargers) for less oil burnoff and reduced chances of damaging oil passageway clogging. Increased horsepower and torque due to less initial drag on engine   Disadvantages The disadvantages of synthetic motor oils include: Potential decomposition problems in certain chemical environments (predominantly in industrial use.) Potential stress cracking of plastic components made of polyoxymethylene (POM) in the presence of polyalphaolefin (PAO). In July 1996, Consumer Reports published the results of a two-year motor oil test involving a fleet of 75 New York taxi cabs and found no noticeable advantage of synthetic oil over regular mineral oil. In their article, they noted that "Big-city cabs don't see many cold start-ups or long periods of high-speed driving in extreme heat. But our test results relate to the most common type of severe service - stop-and-go city driving." According to their study, synthetic oil is "worth considering for extreme driving conditions: high ambient temperatures and high engine load, or very cold temperatures."  Synthetic oils are not recommended in automotive rotary engines (something to bear in mind if you also own an old Mazda MX7 in addition to your Corvette).