How To Pick The Right Motor Oil For Your Car. Choosing the correct motor oil for your car might seem daunting but the best way to start is by checking out the starburst symbol that indicates the oil has been tested and meets the standards of the American Petroleum Institute (API). In addition, there's a 2-character service designation on the container. API's latest service standard is "SL." SL refers to a group of laboratory and engine tests, including the latest series for control of high-temperature deposits. Your third task is to pick the viscosity (thickness) that's suitable for the temperatures your vehicle normally operates in (check your owners manual), and you're done. Well, not quite. There's a whole lot more to the story than that.