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Motor Oil Specifications

An ever-changing alphabet soup

To many consumers, motor oil seems like the most over-certified product on the market. Some bottles of motor oil bear certification from the American Petroleum Institute (API), the European Automobile Manufacturers’ Association (ACEA), and the International Lubricant Standardization and Approval Committee (ILSAC). A reason for these multiple certifications is the ever-increasing emphasis on reducing vehicle emissions and improving fuel economy, while simultaneously increasing engine power and life. Precise performance from motor oil is required to meet these conflicting goals.

Seals of Approval

Here’s a specific example: Phosphorus in motor oil reduces engine wear, especially in areas of extreme pressure. But phosphorus is bad for catalytic converters, so substances such as molybdenum are partially replacing it. However, rarely is an ingredient an exact substitute for another: It may cost more, be less durable, or create its own issues.

The most well-known motor oil standard was originally developed by the Society of Automotive Engineers (SAE) to measure the oil’s viscosity or how well it flows at cold or hot temperatures. Popularly called the oil’s “weight” or “grade,” the SAE requirements are now part of the other certification processes. If tested both cold and hot, two numbers, such as 5W-30 or 10W-40, describe the grade and the oil is called a multi-grade. Single-grade motor oils are measured at only one temperature and should be limited to engines you don’t care much about, such as your neighbor’s lawnmower.

Test Numbers

The first number of a multi-grade oil comes from cold tests and is followed by a “W”, which stands for winter. The smaller the number preceding the “W”, the lower the test temperatures and the lower the temperature at which the oil will still properly lubricate your engine. The second number comes from tests performed at 100 and 150 degrees Celsius. The higher this number, the higher the temperature at which the oil will still properly lubricate your engine.

Without special viscosity additives, oil won’t perform well at both high and low temperatures: An oil without these special additives that maintains its lubricating properties at 230 degrees becomes thicker than ketchup before you’d need a light jacket. The frequently automaker-recommended 5W-30 is no thicker than a 5W grade oil when it’s well below freezing and no thinner than a 30 grade oil when the engine is up to full temperature. This means the oil will remain both thin enough when it’s really cold and thick enough during normal operation. It’s best to stick with your automaker’s SAE grade recommendations, unless you have extra-special needs—and knowledge.

Viscosity Standards

Understanding the viscosity standards are a breeze when compared to figuring out those from the rest of the API tests, well as those from ACEA and ILSAC. Here’s all most consumers need know: Make sure the oil you buy meets—or exceeds—your vehicle maker’s requirements. For vehicles sold in the U.S., this is most often an API standard. API specs are set as a cooperative effort between the oil industry and vehicle and engine manufacturers from the U.S. and Japan. If your carmaker specifies an API standard, look for the API “donut” or “starburst” on the oil container.

To decode the API donut, first look in the center. There is listed the SAE viscosity. Then notice the top half of the donut where API lists what it calls the “performance level”. It’ll say “API SERVICE” followed by “SL” or “SM”, if the oil is designed for a gasoline engine. (Those designed for diesel engines have a “C” rather than an “S”.) “SL” is recommended only for vehicles from 2004 and before. “SM” was introduced as the top standard in 2004 and API says it’s good for all gasoline-engined vehicles until a new standard appears.

Performance Properties

Each API performance level includes the performance properties of all prior categories. The bottom half of the API donut will either be blank or say “Energy Conserving.” Energy Conserving oils do reduce fuel consumption, however, since our driving habits can have an even bigger effect, typically the benefits of Energy conserving oils can only be seen when looking at a large number of vehicles over many miles.

Some API SM oils may also meet ILSAC’s GF-4. If so, it will say so and there will be the API Starburst logo on the front of the container. Additionally, oils may meet an ACEA standard and if so, it’ll say so on the bottle.

Car and oil companies have been working on a new ILSAC standard—to be called GF-5. This is scheduled to appear in 2011 model-year vehicles, replacing 2004’s GF-4. The car companies have a long list of performance requirements they want improved, some of which required designing new tests. For oil companies, the largest challenge may be making GF-5 workable in 2010 and earlier engines, while meeting the automakers’ new desires. Whether legitimate or not, some vintage-car and hot-rod owners already complain about how GF-4-spec oil performs in their vehicles.

If GF-5 can’t be used in older vehicles, imagine the headaches for auto parts stores, quick-lube places, and do-it-yourselfers. We’re sure the oil-company chemists already can.