Volatization is a term used to describe what happens to a fluid when it is heated to the point it begins to "boil off." Upon reaching a certain temperature, oil will begin to lose some of its lighter weight molecules as they vaporize and leave heavier weight molecules behind. Not only does this cause higher oil consumption, it causes increased viscosity, making the oil more difficult to circulate through the lubrication system. The thicker oil left behind after volatization contributes to damaging deposits, sticky piston rings and oil blow-by, all of which contribute to reduced engine life, reduced fuel economy and increased air pollution.
At one time it was not uncommon for typical conventional oils to experience 20-30 percent boil-off in the NOACK Volatility Test. Today’s API standard for SM and SN oils is 15 percent, putting greater demands on oil manufacturers. Premium synthetic oils are significantly more resistant to these effects, with some of the best in the 4.5 to 6 percent range.