Maintaining an appropriate oil level inside the cavity, that is, neither too high nor too low, is a technique that is frequently overlooked. To avoid reliability issues, the sight glass must be halfway full. A half-full sight glass indicates that the oil level is in the center of the bottom-most ball of the bearing. If the oil is overfilled, the bearing will overheat and wear out faster. Underfilling the cavity will result in insufficient lubrication and bearing failure.