The Petroleum Quality Institute of America

The labels include two important pieces of information to determine if an engine oil is appropriate for use in your vehicle. The first piece of information speaks to viscosity grade. The Society of Automotive Engineers (SAE) defines a numerical system for grading motor oils according to viscosity. The suffixes (0, 5, 10, 15 and 25) followed by the letter W designate the engine oil's "winter" grade.

Look to your owner's manual. It specifies the viscosity grade required for your car's engine. Today, the most common grades are 5W-30 and 10W-30.

Watch for the "W"

Whereas the labeling on the bottle of engine oil may suggest the product is a 5W-30, note, if there is no "W" between the 5 and the 30 it may not be a 5W-30. As an example, a SAE 5-30 is not the same as an SAE 5W-30.

The next 'code" to look for is the API Service Classification. Although it might appear complicated to understand at the start, it is really a simple system to get your arms around. Think of it this way, when cars were first built, the oil they required needed an API SA Service Classification. From there, it moved to SB, SC, SD, and so on (skipping only SI and SK). The current API Service Classification is SN.  

So if you buy an engine oil meeting only API SA, it's an engine oil formulated for use in vehicles built in the 1920s. And SA is not hard to find mixed in with SM on the shelves at c-stores and others. Furthermore, it's also not hard to find SF, SJ and other API Service Categories on the shelves. Also, don't let price guide you. Engine oils with a Service Classification prior to SN (including SA) are often priced close to that of API SN. 

The service rating of passenger car and commercial automotive motor oils is classified by the American Petroleum Institute (API). The program certifies that an oil meets certain Original Equipment Manufacturer (OEM) quality and performance standards. The service rating is shown in the API "Service Symbol Donut" on the product label.

The labels include two important pieces of information to determine if an engine oil is appropriate for use in your vehicle. The first piece of information speaks to viscosity grade. The Society of Automotive Engineers (SAE) defines a numerical system for grading motor oils according to viscosity. The suffixes (0, 5, 10, 15 and 25) followed by the letter W designate the engine oil's "winter" grade.

Look to your owner's manual. It specifies the viscosity grade required for your car's engine. Today, the most common grades are 5W-30 and 10W-30.

Watch for the "W"

Whereas the labeling on the bottle of engine oil may suggest the product is a 10W-30, note, if there is no "W" between the 10 and the 30 it may not be a 10W-30. As an example, a SAE 10-30 is not the same as an SAE 10W30.

The next 'code" to look for is the API Service Classification. Although it might appear complicated to understand at the start, it is really a simple system to get your arms around. Think of it this way, when cars were first built, the oil they required needed an API SA Service Classification. From there, it moved to SB, SC, SD, and so on (skipping only SI). The current API Service Classification is SM.

So if you are buying an SA oil, it's an engine oil formulated for use in vehicles built in the 1920s. And SA is not hard to find mixed in with SM on the shelves at c-stores and others. Furthermore, it's also not hard to find SF, SJ and other API Service Categories on the shelves. Also, don't let price guide you. Engine oils with a Service Classification prior to SM (including SA) are often priced close to that of SM.