Gear oils are not correctives for abrasive wear because here the action is due to hard particles between the gear face as they mesh. If the abrasive is due to loose metal, sand, etc; gear oils may wash the foreign particles from the moving areas, but unless the abrasives settle out they will continue to act as lapping compounds. However, if the viscosity of the gear oil is low, the large foreign particles may be deposited in areas where the velocity of the oil is low, and thus they will be harmless.
The best corrective for abrasive wear of gears is to drain and flush out the gear case and refill with clean oil. Circulating oil systems used for gear oils can be equipped with filters or strainers. Likewise, a settling period can be provided in the storage system for the fluid. Some gear cases in automotive vehicles have magnetized drain plug so that most iron or steel particles will become attached as the gear oil circulates. Where vehicles operate under conditions promoting dust, as do many tractors, it is wise to drain gear cases frequently so that abrasives filtering into the gear oil will be removed.
