Classify oils according to SAE

Single grade oil:

For example: SAE 30 (single grade oil with viscosity 30 for summer)

Multi-level oil:

For example: SAE 10W30 (this is a multi-grade oil for both high and low temperatures. W – winter: winter.)
This oil helps oil bearing bearings lubricate when the engine temperature is low. This is especially noticeable when it’s cold.