Roller cone drill bit with bit condition monitoring and alert system

A roller cone drill bit with built in monitoring and alert system has a lubricant compensator assembly 61 that communicates with the roller cone bearing surface 99 via lubricant passageways 91, 95. Sensors 213 in the bit monitor the characteristics of the lubricant, particularly its electrical conductivity, to detect changes related to bearing wear or seal failure. The lubricant characteristics are monitored and an alert system is triggered if they fall outside of set parameters. Both the monitoring and alert systems are controlled by a separate control system. An annular capacitor may be used to detect changes in the dielectric constant of the lubricant.