Only the oil portion lubricates. Formulators have said that in as little as 2,400 hours of use, even the finest lubricating oils deteriorate below minimum lubricant specifications. It is the eventual loss of these additives that make frequent oil changes necessary. As an alternative to mineral oils, synthetic lubricants have been developed that have proven to be vastly superior to conventional petroleum products. Petroleum lubricants are a blend of large, viscous molecules and distillates from the crude that are thin and unstable.
Synthetics are uniform and homogeneous in nature.
They do not evaporate or oxidize. Many synthetic lubricants, properly kept uncontaminated, will perform under normal operating conditions for two years or longer. This extended operating range negates the objection to the higher initial cost of the synthetic product. Even though the bearing is quite heavily loaded, the expected life is off-scale compared to real world experience. The fatigue life calculation assumes perfect lubrication.