Each Mark conveys information that can be used by the consumer. The center identifies the oil's viscosity. The bottom half tells whether the oil has demonstrated energy-conserving properties in a standard test in comparison to a reference oil. The current API performance categories that can appear in the top part of the donut are listed in the API Service Category Chart. The center of the donut shows the oil's SAE viscosity grade.
Viscosity is a measure of an oil's flow characteristics, or thickness, at certain temperatures.
The lower the number the more easily the engine will start in cold weather. Operators should refer to their owners manuals to select the proper viscosity oil for the ambient temperature and operating conditions at which the equipment will be used. The bottom of the donut tells whether the oil has energy conserving properties when compared with a reference oil in an engine test. Widespread use of engine oils with this designation should result in an overall saving of fuel in the nation as a whole, but a particular vehicle operator may not experience a fuel savings as a result of using these oils. To view a complete listing of oil service categories for gasoline and diesel engines, click here.