Bearing life is a major component in overall fan life. Maintaining proper lubricant levels with appropriate lubricant for the application will extend bearing life and require fewer replacements. A simple preventative maintenance program implemented for your fan can save thousands of dollars in replacement parts over the course of several years. Such a plan would involve such steps as regular lubrication of fan and motor bearings, connection inspections, and vibration analyses.
Read the following article from POWER Magazine for an overview of the various types of lubricant additives and their functions.
http://www.powermag.com/all-about-lubricant-additives/
Header picture source: Lubricants and Sealants: 3 Common Signs of Bearing Failure
Table source: Nye Lubricants Inc.