Changing the oil at the correct time interval is the key to achieving a long working life of the components in the gearbox. Only by ensuring a reasonable oil change interval, can the lubricating and protective properties of lubricating oil be used. Under normal circumstances, it should be based on the maintenance period recommended by the manufacturer of the wheel loader, but this can only be relative and must be combined with the results of the oil sample extraction analysis to know the actual working conditions. For example, the maintenance manual requires that the oil change interval of the gearbox is 500h. According to the operating conditions of the loader, we sample and analyze the oil samples every 250h or 100h to determine when to change the oil. However, when the lubricating oil is used for 1000h, we should replace it immediately. In addition to regular replacement of new oil, if the oil is found to be deteriorated or mixed with impurities during usual inspections, it should also be cleaned and inspected and replaced with new oil.