As discussed in the Base Oils & Lubricant Performance thread, one area where one can see a performance advantage in base stock characteristics is in a lubricants ability to resist thermal break down. This can be demonstrated by the American Society for Testing and Materials (ASTM) and their Noack Volatility test, otherwise known as the D-5800.


Quote Originally Posted by Amsoil, Inc. (06/2003)
Oil volatility is the measure of how susceptible oil is to boil-off under high heat conditions. Petroleum oils experience significant boil-off during high temperature engine operation and subsequently higher oil consumption. Evaporation loss contributes to damaging deposits, sticky piston rings and oil blow-by, resulting in a drag on performance and reduced engine life. Synthetic oils are far more impervious to this kind of degradation. The lower volatility of synthetics is another reason they are also better for the environment than conventional products.
Base Oil Comparison

A lower Noack Volatility number equates to a lower percentage evaporation loss of the motor oil. Evaporation loss is one reason for having to add motor oil to your car even when there are no oil leaks present. This evaporation loss can also be the cause of a motor oil thickening over an Oil Change Interval (OCI). The ability of PAO base oils to resist volatility break-down can give them an increased value over conventional motor oils due to increased oil change interval capabilities.

Lubricant #1: Conventional Motor Oil

Chevron Supreme SAE 10W-30 API (SM)
API base stock category: Group II
Base Stock Origin: Refined from crude oil.

ASTM D-5800 Noack Volatility: 9.12 (Amsoil test result, June 2005)

Lubricant #2: Full Synthetic Motor Oil

Pennzoil Platinum SAE 10W-30
API base stock category: Group III
Base Stock Origin: Refined from crude oil.

ASTM D-5800 Noack Volatility: 9.9 (Pennzoil Typical Physical and Chemical Properties Sheet, February 2008)

Lubricant #3: 100% Synthetic Motor Oil

AMSOIL 100% Synthetic SAE 10W-30 Motor Oil
API base stock category: Group IV/V
Base Stock Origin: Pure chemicals derived from Crude Oil or Natural Gas.

ASTM D-5800 Noack Volatility: 5.4 (Amsoil Typical Technical Properties Sheet, October 2007)