How long is the oil retention period?

The maintenance period of the oil is generally two years. The engine oil has the effect of mechanical lubrication. 

While the oil also has a certain maintenance period, the physical chemical properties of the oils stored for long periods of time may change, 

resulting in the condition of the lubricant worsening during the operation of the machinery. 

This is likely to cause damage to the components of the machine, so the oil needs to be replaced regularly.