Motor oil can be segmented into four basic varieties—synthetic oil, synthetic blends, high mileage oil, and conventional oil.
Synthetic Motor Oil
Synthetic motor oil has gone through a chemically engineered process. Synthetic oil molecules are more uniform in shape with fewer impurities and better properties than conventional oil molecules. In general, synthetic oil has better extreme high temperature and low temperature performance. Synthetic oils are generally formulated with higher performing additives.
Synthetic Blend Motor Oil
Synthetic blend motor oil uses a mixture of synthetic and conventional base oils for added resistance to oxidation (compared to conventional oil) and provide excellent low-temperature properties.
High-Mileage Motor Oil
High-mileage motor oil is specially formulated for late model vehicles or newer vehicles with over 75,000 miles. High mileage motor oil, with its unique additives and formulation, helps to reduce oil burn-off, and helps prevent oil leaks that may occur in older engines.
Conventional Motor Oil
Conventional motor oils can be formulated in a range of viscosity grades and quality levels. Conventional motor oil is recommended for drivers with simple engine designs and regular (as opposed to severe) driving styles.
Motor Oil Grade Designations
Motor oils use a rating system developed by the Society of Automotive Engineers (SAE), to classify oil by viscosity. Viscosity is a fluid’s resistance to flow. Fluids that are thin (like water) have a low viscosity, and fluids that are thick (like honey) have a high viscosity. Motor oil also changes in viscosity measurement as it is heated or cooled.
Multi-grade viscosity motor oils are able to perform at a wide range of temperatures. For an SAE 0W-20 oil, the “0” is the cold-temperature viscosity rating (the “W” stands for “Winter”), and the “20” is the high temperature viscosity rating. Multigrade viscosity motor oil flows well at low temperatures, but still protects the engine at high temperatures.
For comparison’s sake, SAE 5W-30 and SAE 0W-30 will flow better at colder temperatures than SAE 10W-30, while still providing protection at higher temperatures.
Always follow the vehicle owner’s manual to determine the correct motor oil specification, viscosity grade, and oil drain interval for your engine.
The API/ILSAC “Starburst”
This symbol is shown on quality motor oils that meet current minimum industry requirements. API is an acronym for the American Petroleum Institute. The institute’s Starburst stamp of approval—“American Petroleum Institute Certified”—was created to help consumers identify engine oils that meet minimum performance standards set by vehicle and engine manufacturers.
The Starburst identifies engine oils recommended for a certain application, such as “For Gasoline Engines.” To carry this symbol on the container, the oil must meet the most current requirements of ILSAC, which is the International Lubricant Standardization and Approval Committee, a joint effort of U.S. and Japanese automobile manufacturers.The API/ILSAC Starburst is found on the front label of qualified motor oil bottles.
The API “donut”
Another identifier on motor oil containers is the API “donut” typically found on the back label. It’s divided into three parts. The top half of the circle (2) indicates the API service rating, also called the performance level. The center of the circle (3) denotes the SAE viscosity, which we just discussed. The lower half of the circle (4) indicates whether the oil has demonstrated certain resource conserving or energy-conserving properties.
In the top part of the donut, the words “API Service XXXXX” (5) indicate the type of engine and performance the oil provides. API Service SN the current rating means “S” for Service Station oil (for gasoline engines) and N the current level of service. Or it will say “API Service CJ-4.” API service CJ-4 means “C” for commercial engines (diesel engines) and J-4 where J is the current performance level and 4 indicates a 4-stroke diesel (a 2 will be used for 2-stroke diesel engines).
Check your owner’s manual for the recommendation for your vehicle. The API Service Ratings are backward-compatible, so older vehicles can use the current designation.