These symbols mean that the oil has been certified by the API. The manufacturer only recommends API trademark oils.
The API Starburst trademark
certifies 0W-20, 0W-30 and 5W-30 engine oils.
The API Donut trademark certifies 0W-40 and
5W-40 engine oil.
For diesel engines, oils with a high ash content may produce damaging deposits on cylinder head valves and/or after treatment system damage. A maximum sulfated ash content of 1.00 mass % is recommended for all oil used in the engine.
The same oil change interval is to be followed for synthetic oil as for petroleum-based oil. Also, synthetic oil must meet the same performance specifications as petroleum oil.
Do not use chemical flushes in your engine oil as the chemicals can damage your engine. Such damage is not covered by the New Vehicle Limited Warranty.