Oil ratings explained

The American Petroleum Institute’s Service Symbol “Donut” is divided into three parts: The top half describes the oil’s performance level; the center identifies the oil’s viscosity; and the bottom half tells whether the oil has demonstrated energy-conserving properties that could result in fuel savings in vehicle fleets. Most automobile manufacturers recommend oils that carry the API Certification Mark.

The oil’s Performance Level is rated for gasoline and/or diesel engines. The letter “S” followed by another letter (for example, SL) refers to oil suitable for gasoline engines. The letter “C” followed by another letter and/or number (for example, CH-4) refers to oil suitable for diesel engines. These letters officially stand for “Service” and “Commercial.”

The Viscosity Rating is a measure of an oil’s flow characteristics, or thickness, at certain temperatures. The low-temperature viscosity (the first number, 5W in a 5W-30 oil) indicates how quickly engines crank in winter and how well the oil will flow to lubricate critical engine parts at low temperatures. The lower the number, the more easily the engine will start in cold weather. The high-temperature viscosity (the second number, 30 in a 5W-30 oil) provides thickness, or body, for good lubrication at operating temperatures.

Always refer to your owner’s manuals to select the proper viscosity oil for the ambient temperature and operating conditions at which the equipment will be used.

A multigrade oil provides good flow capability for cold weather but retains thickness for high-temperatures.