Lubrication/wear protection: How well does the oil lubricate and prevent
wear? The chemical makeup of synthetics results in a superior lubricating
film. Additionally, the thermal stability of synthetic oils maintains a
protective oil film in much more severe conditions and at higher
temperatures than petroleum. In standard anti-wear testing such as the Shell
four-ball wear test, some synthetics achieve up to four times the wear
protection when compared to petroleum oils. When higher temperatures and
pressures are used in such tests, the results significantly favor synthetic oils.
Under Normal Conditions
Advantage: Slight for synthetics
Under Severe Conditions
Advantage: Very strongly synthetics
Oil life/endurance: How long can the oil provide proper lubrication and
perform all required functions? Oil life is a function of time and severity of
service and can vary from vehicle to vehicle. Oil is said to be condemned,
that is, not fit for continued service, when one or more of the following
conditions exist:
- Viscosity has decreased by one grade or increased by more than one grade
- Fuel contamination is greater than 3 percent
- Soot level exceeds 4 percent
- Total dissolved solids are greater than 4 percent
- Total base number is less than two
- Critical additives are depleted
- Oxidation number greater than 50 (30 for petroleum)
- Nitration number less than 50 (30 for petroleum)
As explained above, synthetic oils are less likely to thicken as the result of
vaporization or oxidation and stay in proper viscosity grade for significantly
longer periods of service. Several of the other factors for condemnation are
the same for either synthetic or petroleum oils and are more dependent on the
quality and concentration of chemical additives to continue to provide
service. Soot and total dissolved solids are products of engine combustion