Even if your manual doesn't insist on full synthetic engine oil, it's still a smart choice, as synthetic engine oils offer the best possible protection for all engines.
Why would you choose full synthetic engine oil? After all it's the most expensive option, and the chances are that the manufacturer of your vehicle doesn't even insist on you using full synthetic engine oil in order to keep your warranty valid.
The fact is that if you want to offer your engine the best possible protection, it's worth exceeding the standard asked for by the auto manufacturer and going for full synthetic engine oil. Even if your manual doesn't recommend full synthetic, you can be assured that it's the best option for your engine. That's because synthetic motor oil is the most highly refined engine oil you can buy, delivering optimum protection from the moment you start the key, and working harder in all scenarios that put stress on an engine, such as driving in extreme temperatures, towing heavy loads and sitting in stop-go traffic. Depending on the viscosity your manual recommends, synthetic oil can also improve the performance and fuel economy of your vehicle, and will even stay stronger for longer between drain intervals than traditional mineral or part synthetic oils.
(Originally posted on https://www.castrol.com/en_za/south-africa/home/car-engine-oil-and-fluids/car-maintenance/why-you-should-use-synthetic-oil.html)