Synthetic oils, albeit more expensive than conventional oils, are significantly better virtually in all aspects. The conventional point of view espoused by many mechanics that it is best to change standard motor oils frequently no longer applies as longer lasting synthetic oil is likely to provide far better overall engine protection. Specific measurable benefits of synthetic oils include cold cranking properties, low volatility, and oxidation resistance. In winter, the cold cranking viscosity of engine oil determines the lowest temperature at which an engine can be started. At minus 22 ºF (minus -30ºC) the cranking requirements of synthetic oils are nearly one third of Group II base oils. The Noack Volatility test measures the evaporation of oil at operating temperature, the consequence of which is an increase in oil viscosity and drag on the engine. Synthetic base oils have less than half the evaporation rate of Group II oils. Oxidation of oil determines how long the oil can be used, and a useful way to measure this is the Turbine Oil Stability Test. Synthetic oils perform much better than Group I and II oils. Synthetic oils contain hardly any sulfur, unstable hydrocarbons, or other trace impurities. Consequently, the oil is stable in use and produces hardly any harmful deposits. The oil is free flowing, so it circulates immediately at startup, providing faster and better startup protection during the critical period when most engine wear occurs.