The paper address the tests required to be conducted for lubrication oil. It investigates the change of properties of new oil after it is being used for flushing. The recommendations of changing flushed oil or keeping it made on different analysis and studies, however, if the oil properties are not changing, then using the flushed oil is recommended as the new oil will not be as clean as flushed oil. The paper listed several oil cleaning methods and highlighted several causes which could result on bearing failure. The bearing lifetime was discussed and how the impact of different parameter could impact the bearing life span if it is generating additional forces, for example, due to the increase of friction force which contribute to the equivalent dynamic bearing load.