How frequently oil changes are needed depends mainly on the operating conditions and the quantity of oil.
With the oil bath lubrication method, it is generally sufficient to change the oil once a year, provided the operating temperature does not exceed 50 °C (120 °F) and there is little risk of contamination. Higher temperatures require more frequent oil changes, e.g. for operating temperatures around 100 °C (210 °F), the oil should be changed every three months. Frequent oil changes are also necessary if other operating conditions are arduous.
With circulating oil lubrication systems, the period between oil changes is also determined by how frequently the total oil quantity is circulated and whether or not the oil is cooled. It is only possible to determine a suitable interval through testing and regular inspection to see that the oil is not contaminated or excessively oxidized. The same applies for the oil jet lubrication method. With the oil-air lubrication method, the oil only passes through the bearing once and is not recirculated.