SAE Viscosity Grade

The labels include important 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.

 API Service Categories

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 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).

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 SN 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.

OEM Specific Performance Specifications

Although the majority of vehicles currently on the road in the US specific the use of motor oils meeting a specific API Service Category, some vehicle manufacturers require use of lubricants that meet the original equipment manufacturer's (OEM) specifications. General Motor’s dexos is one example. Click for more about the dexos specification. Always check the labels on the motor oils purchased to assure they include any OEM specifications required in your vehicle.

Read the labels on the oils you buy, ask questions when you have your oil changed and read your car owner's manual.

Always consult your vehicle owner's manual to determine what motor oil you should use, and READ THE LABELS ON THE OIL YOU BUY.