The recommended engine oil grade for older models of the TVS Apache RTR 160 motorcycle is SAE 10W30. It is advised to use fully synthetic oil with API-SL and JASO MA2 specifications for better performance and engine life. Alternatively, semi-synthetic 10W30 or fully synthetic 10W40 grade engine oil can also be considered, but it is crucial to stick to the viscosity grade recommended by TVS for optimal performance and longevity of the engine[5).