It is important to know how to read the labels and what to look for on both the front and back labels of the motor oil you buy, or you may be using product that can cause unsatisfactory performance or damage to your engine. The following are some key items to look for on motor oil labels and to consider before buying.
American Petroleum Institute (API) Service Symbol “Donut”
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 quality and performance standards. The service rating is shown in the API "Service Symbol Donut" on the product label, usually found on the back label.
The label includes two important pieces of information to determine if an engine oil is appropriate for use in your vehicle.
Oil Viscosity
The first piece of information speaks to viscosity grade. Viscosity is simply the resistance of a fluid to flow. A higher viscosity implies a slower flow and a thicker fluid. The viscosity changes with temperature to ensure protection and operability under all circumstances. Thus, the viscosity index measures the ability of an engine oil to resist becoming thinner at high temperatures. conventional oils incorporate additives to change its viscosity.
The Society of Automotive Engineers (SAE) defines a numerical system for grading motor oils according to viscosity.
Multi-viscosity motor oils are designated by two numbers – the first set of numbers (0, 5, 10, 15 and 25), is indicative of how the oil flows at low temperatures and is followed by the letter W to designate the engine oil's "winter" grade. The second set of numbers indicates how the oil flows at higher/operating temperatures. This is important since oil naturally thickens when cold and thins when hot. If the grade listed is not preceded by “SAE” and/or there is no “W-” between the first and second number, it may not be a multi-grade. As an example, a 5-30 is not the same as an SAE 5W-30.
You should be aware of changes in weather and climate to keep your engine fully functional. Here you can see the recommended oil for each ambient temperature:
Multi-viscosity (aka multi-grade) motor oils are most commonly recommended for use in vehicles currently on the road.
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 10W30.
API Service Classification
Viscosity characteristics, are the first and most important element of the classification and labeling of motor oils, but viscosity is not the only factor to consider when choosing a motor oil. The second thing to look for on the API donut is the service classification which helps determine the right ratio of oil properties to its operating conditions.
Motor Oil Service Classification for Gasoline Engines
The classification works this way; early in the automotive industry, The first API Service Classification of motor oil was SA. From there, as motor oil improved and met increasing specifications for newer cars, the classification moved to SB, SC, SD, and so on (skipping only SI and SK).
If you buy a motor oil meeting only API SA, it's a motor oil formulated for use in gasoline engine vehicles built in the 1920s. You can use newer motor oil with a more recent API rating. Newer motor oil blends are backwards compatible. That means they work just fine in older engines. You can’t say the same thing about older API ratings. They’re not compatible with newer engines. It’s because motor oil with older API ratings can’t handle the heat generated by newer engines. Heat causes the oil to degrade quickly, and once it degrades it can’t lubricate the engine well enough. If you use motor oil with an API rating for engines older than yours, your engine will wear prematurely. Because SA or other obsolete API Service Categories are sometimes mixed in with SN on the shelves, it is vital to read the API label carefully. Also, don't let price guide you. Motor oils with a Service Classification prior to SN (including SA) are often priced close to that of API SN.
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American Petroleum Institute |
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Category |
Status |
Service |
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SP |
Current |
Introduced in May 2020, designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, and more stringent sludge and varnish control. API SP with Resource Conserving matches ILSAC GF-6A by combining API SP performance with improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85. |
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SN |
Current |
For 2010 and older automotive engines. Introduced in October 2010, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conserving matches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control system compatibility, and protection of engines operating on ethanol-containing fuels up to E85. |
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SM |
Current |
For 2010 and older automotive engines. |
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SL |
Current |
For 2004 and older automotive engines. |
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SJ |
Current |
For 2001 and older automotive engines. |
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SH |
Obsolete |
CAUTION - Not suitable for use in most gasoline-powered automotive engines built after 1996. May not provide adequate protection against build-up of engine sludge, oxidation, or wear. |
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SG |
Obsolete |
CAUTION - Not suitable for use in most gasoline-powered automotive engines built after 1993. May not provide adequate protection against build-up of engine sludge, oxidation, or wear. |
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SF |
Obsolete |
CAUTION - Not suitable for use in most gasoline-powered automotive engines built after 1988. May not provide adequate protection against build-up of engine sludge. |
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SE |
Obsolete |
CAUTION - Not suitable for use in gasoline-powered automobile engines built after 1979. |
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SD |
Obsolete |
CAUTION - Not suitable for use in gasoline-powered automobile engines built after 1971. Use in more modern engines may cause unsatisfactory performance or equipment harm. |
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SC |
Obsolete |
CAUTION - Not suitable for use in gasoline-powered automobile engines built after 1967. Use in more modern engines may cause unsatisfactory performance or equipment harm. |
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SB |
Obsolete |
CAUTION - Not suitable for use in gasoline-powered automobile engines built after 1951. Use in more modern engines may cause unsatisfactory performance or equipment harm. |
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SA |
Obsolete |
CAUTION - Not suitable for use in gasoline-powered automobile engines built after 1930. Use in more modern engines may cause unsatisfactory performance or equipment harm. |
Motor Oil for Diesel Engines
The API C-series classifications pertain to diesel engines. The “C” stands for compression ignition systems, which is how diesel engines operate. The C- Series contains API CK-4 (most Recent), CJ-4, CI-4 PLUS, CI-4, and CH-4 oils. Driven by federal regulations that raise the bar for fuel economy while lowering emission limits, modern diesel vehicles produce more horsepower and torque than ever. They run much hotter, operate under higher pressures and have the ability to burn up to 20 percent biodiesel. These advances place new demands on diesel oil, in addition to the demands for increased protection from those who depend on diesel power to make a living. New classifications are introduced when new technology or standards require reformulation of oils to protect modern diesel engine.
FA-4 Class
The new FA-4 classification pertains only to some 2017 and newer diesel engines mostly in over-the-road trucks. API FA-4 oils are not interchangeable or compatible with API CK-4, CJ-4, CI-4 PLUS, CI-4, and CH-4 oils. Consult your Owners manual for the correct oil.
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American Petroleum Institute |
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Category |
Status |
Service |
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CK-4 |
Current |
API Service Category CK-4 describes oils for use in high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or oil drain interval. These oils are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used. API CK-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase. API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 and can effectively lubricate engines calling for those API Service Categories. When using CK-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval recommendations. |
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CJ-4 |
Current |
For high-speed four-stroke cycle diesel engines designed to meet 2010 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or drain interval. API CJ-4 oils exceed the performance criteria of API CI-4 with CI-4 PLUS, CI-4, CH-4, CG-4 and CF-4 and can effectively lubricate engines calling for those API Service Categories. When using CJ-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval. |
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CI-4 |
Current |
For high-speed four-stroke cycle diesel engines designed to meet 2010 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or drain interval. API CJ-4 oils exceed the performance criteria of API CI-4 with CI-4 PLUS, CI-4, CH-4, CG-4 and CF-4 and can effectively lubricate engines calling for those API Service Categories. When using CJ-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval. |
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CH-4 |
Current |
Introduced in 1998. For high-speed, four-stroke engines designed to meet 1998 exhaust emission standards. CH-4 oils are specifically compounded for use with diesel fuels ranging in sulfur content up to 0.5% weight. Can be used in place of CD, CE, CF-4, and CG-4 oils. |
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CG-4 |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 2009. |
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CF-4 |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 2009. |
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CF-2 |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 2009. Two-stroke cycle engines may have different lubrication requirements than four-stroke engines, so the manufacturer should be contacted for current lubrication recommendations. |
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CE |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 1994. |
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CD-II |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 1994. |
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CD |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered automotive engines built after 1994. |
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CC |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered engines built after 1990. |
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CB |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered engines built after 1961. |
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CA |
Obsolete |
CAUTION - Not suitable for use in most diesel-powered engines built after 1959. |
Motor oils are not required to be licensed or certified by the API. However, some motor oils may meet the requirements for current API specifications without such certification. If the “Donut” is not displayed on the label, consumers are relying solely on the trust they have in the motor oil manufacturer. Again, checking the vehicle owner’s manual is advised since many car manufacturers recommend motor oil licensed by the American Petroleum Institute.
While the majority of vehicles currently on the road in the U.S. specify the use of motor oils meeting API specifications, some vehicle manufacturers require use of lubricants that meet their own specifications. Always check the labels on the motor oils purchased to assure they include any manufacturer specifications required in your vehicle.
API “Starburst”
The API “Starburst” is another symbol to look for and is found on the front motor oil label. The presence of this symbol indicates that the motor oil is formulated to meet the most current International Lubricant Specification Advisory Committee (ILSAC) standards which include additional requirements for fuel economy and emission system protection.
Although the “Starburst” is not required on motor oil labels, check your owner’s manual as it may specify use of motor oil bearing the “Starburst” symbol.
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