Is 5w40 Fully Synthetic Oil?

[StHannah]

5w40 is the viscosity grade of engine oil, and the grade alone cannot determine whether it is fully synthetic oil. Methods to identify synthetic oil: Check if it is labeled as PAO or ester-based oil. Only products made from these two raw materials without blending with Group I, II, or III base oils are fully synthetic oils. Also, see if the word 'full' precedes 'synthetic oil' on the label. If it is PAO oil or ester-based oil, it will definitely be labeled as fully synthetic oil. Introduction to fully synthetic oil: Fully synthetic oil indeed performs exceptionally well, excelling in cold starts during winter and high-temperature resistance in summer. It also has a long oil change interval and provides maximum protection for the engine. However, due to its thinner oil film characteristics, it is not suitable for older cars with significant wear or budget vehicles with less precise engine machining. Typically, these types of vehicles have larger gaps between engine components, and the thinner oil film of fully synthetic oil cannot provide adequate lubrication, leading to unnecessary wear.