Engine Oil Classification

In principle, there are two types of engine oil classification. They are different but also complementary, and are used to identify a particular product:

• Classification according to viscosity (fluidity).
• Classification according to service category (performance level).

1.1 Classification According to Viscosity

1.1.1 The SAE Standard

The need for a simple international classification system for engine oils led to the establishment of the Society of Automotive Engineers (SAE), which developed a system bearing its name. This system defines viscosity grades only.

Two categories are distinguished: so-called summer oils, designated by the SAE grades 20, 30, 40 and 50, and winter oils, designated by SAE 0W, 5W, 10W, 15W, 20W and 25W.

The latter grades are primarily concerned with the ability of the oil to provide satisfactory performance during cold starts.

The following table summarizes the viscosity limits at the relevant temperatures. Note that summer oils are always evaluated at 100°C, whereas winter oils are evaluated at different, lower temperatures.

SAE grade	Maximum dynamic viscosity (mPa·s or cP)	Pumpability limit	Kinematic viscosity at 100°C (mm²/s or cSt)
0W	3,250 at −30°C	60,000 at −40°C	—
5W	3,500 at −25°C	60,000 at −35°C	—
10W	3,500 at −20°C	60,000 at −30°C	—
15W	3,500 at −15°C	60,000 at −25°C	—
20W	4,500 at −10°C	60,000 at −20°C	—
25W	6,000 at −5°C	60,000 at −15°C	—
20	—	—	5.6–9.3
30	—	—	9.3–12.5
40	—	—	12.5–16.3
50	—	—	16.3–21.9
60	—	—	21.9–26.1

Note: The original table’s formatting is partially disrupted. The values above have been arranged according to the apparent original sequence; the original technical specification should be checked before using these figures for engineering purposes.

A single lubricant may have a viscosity measured at 100°C that places it in one of the five SAE summer grades, as well as a low-temperature viscosity that qualifies it for one of the six winter grades.

In this case, the viscosity grade is indicated by two designations, and the oil is called a multigrade oil, for example, SAE 15W-40.

The viscosity of a multigrade oil varies much less with temperature than that of a monograde oil. It remains sufficiently fluid in cold weather to allow reliable starting and immediate lubrication, while also maintaining a sufficiently high viscosity to ensure a continuous oil film.

The viscosity index of multigrade oils is always greater than 100.

1.2 Classification According to Service Performance

The SAE classification refers only to viscosity and does not provide a definitive indication of an oil’s quality or performance level.

To address this limitation, major organizations such as the API (American Petroleum Institute), the US military (MIL), major vehicle manufacturers such as GM and Ford, and the CCMC (Committee of Common Market Automobile Constructors) developed specifications based on the performance requirements expected of engine oils.

Each specification consists of a series of laboratory tests selected to evaluate the properties of the lubricants being assessed.

The properties evaluated at a given performance level include the following:

– Detergency: The ability of the oil to keep moving engine components clean, particularly piston rings, as well as other components lubricated at high temperatures.

– Dispersancy: The ability of the oil to keep contaminants suspended and remove them when the oil is drained.

– Oxidation resistance: The ability to withstand very high temperatures without the oil deteriorating.

– Wear resistance: A property directly linked to engine service life. Friction modifiers are sometimes used to alter friction characteristics under certain operating conditions. These additives are also used in agricultural tractor oils and automatic transmission fluids (ATF).

– Anti-rust properties: These protect internal engine components, such as bearing shells, against corrosion.

1.3 The Most Common Standards and Specifications

1.3.1 Definition of a Standard

A standard is defined by three elements:

1. The manufacturers’ association: The organization that establishes the procedures and tests required for compliance.
2. The type of standard: The category of lubricant concerned.

Engine lubricants may be intended for:

• Petrol engines.
• Diesel engines in commercial vehicles.
• Diesel engines in passenger cars.

3. The performance level of the standard: This level is indicated by a number or letter. The higher the indicator, the higher the oil’s performance level.

Example: CCMC D5

• CCMC: Name of the organization (European manufacturers).
• D: Diesel standard for commercial vehicles under the CCMC system.
• 5: Performance level of the standard (from 1 to 5 for CCMC D).

1.3.2 Definition of an Approval

An approval is similar to a standard, but the requirements are established by a vehicle manufacturer for its own specific needs.

The manufacturer issues an approval certificate.

Approvals are regarded as quality labels for engine oils.

The best-known manufacturers issuing approvals include Ford, General Motors, VW-Audi, Mercedes-Benz, BMW and Porsche.

For trucks, the principal manufacturers include Mercedes-Benz, MAN and Volvo.

1.3.3 Standards Organizations

1.3.3.1 API: American Petroleum Institute (American Manufacturers)

The first letter identifies the type of standard.

The second letter indicates the performance level, progressing alphabetically. The further along the alphabet the letter appears, the higher the performance level.

• S (Service) category: SA to SJ in the original classification; subsequent categories include SL and SM, followed by SN and later classifications. Intended for petrol engines.
• C (Commercial) category: CA to CF in the original classification, followed by later categories. Intended for diesel engines.

A. API Petrol Engine Categories

Standard	Application	Notes
SA	Petrol engines that do not require additive-treated oil.	No additives, except pour-point depressants and anti-foam agents.
SB	Petrol engines requiring minimum protection against scuffing and oxidation.	Provides some anti-scuffing and antioxidant properties.
SC	Petrol engines, 1964–1967.	Protection against deposits, wear and corrosion.
SD	Petrol engines, 1968–1971.	Similar protection to SC, but at a lower performance level.
SE	Petrol engines, 1972–1980.	Similar protection to SD, but at a lower performance level.
SF	Petrol engines, 1980–1988.	Greater wear and oxidation protection than SE.
SG	Petrol engines, introduced in 1993 according to the source.	Greater protection against deposit formation, wear and oxidation than SF.
SH	Petrol engines, introduced in 1996 according to the source.	Covers the performance requirements of SG but is tested according to the CMA protocol.
SJ	Petrol engines, introduced in 2001 according to the source.	More stringent quality requirements than SH, for example, regarding phosphorus content.
SL	Petrol engines, introduced in July 2001.	Reduced high-temperature deposits and lower oil consumption.
SM	Petrol engines.	Improved oxidation stability, making it suitable for extended oil-change intervals.
SN	Introduced in October 2010 for 2011 model-year vehicles and older vehicles.	Designed to provide improved protection against high-temperature piston deposits, more stringent sludge control and seal compatibility. API SN with Resource Conserving meets ILSAC GF-5 requirements, combining API SN performance with improved fuel economy, turbocharger protection, emissions-control system compatibility and protection for engines running on ethanol-containing fuels up to E85.

B. API Diesel Engine Categories

Standard	Application	Notes
CA	Naturally aspirated diesel engines operating under light loads and using low-sulphur fuel.	1940–1950. Meets MIL-L-2104 A requirements. Contains antioxidants and detergents.
CB	Naturally aspirated diesel engines operating under moderate loads and using low-sulphur fuel.	1949–1960. Supplement 1 level. Provides antioxidants and high-temperature detergents.
CC	Naturally aspirated and mildly supercharged diesel engines operating under moderate loads.	Introduced in 1961. Meets MIL-L-2104 B requirements. Contains antioxidants, detergents and dispersants.
CD	Naturally aspirated and supercharged diesel engines operating under moderate loads.	Meets Caterpillar Series 3 requirements. Contains antioxidants and detergents.
CD-II	Two-stroke diesel engines operating under heavy loads.	API CD performance with a specific test for two-stroke diesel engines.
CE	Highly supercharged diesel engines operating under heavy loads, from 1983 onward.	Introduced in 1987. Meets Mack EOK/2 and Cummins NTC 400 requirements. Contains antioxidants, detergents, dispersants and anti-wear additives.
CF	Diesel engines. Introduced in 1994.	For indirect-injection engines and other engines, including those using fuel containing more than 0.5% sulphur. Can replace CD oils.
CF-2	Diesel engines. Introduced in 1994.	For heavily loaded two-stroke diesel engines. Can replace CD-II oils.
CF-4	Diesel engines. Introduced in 1990.	For high-speed engines, with or without supercharging. Can replace CD and CE oils.
CG-4	Diesel engines. Introduced in 1995.	For heavily loaded, high-speed engines operating on diesel fuel containing less than 0.5% sulphur. Suitable for 1994 emissions standards. Replaces CD, CE and CF-4 oils.
CH-4	Diesel engines. Introduced in December 1998.	For heavily loaded, high-speed engines meeting 1998 emissions standards and operating on diesel fuel containing less than 0.5% sulphur.
CI-4	Diesel engines meeting the emissions requirements introduced in 2004 and using low-sulphur diesel fuel.	In force from March 2003, according to the source. The original text is incomplete regarding the fuel-sulphur limit.
CI-4 PLUS	Introduced in 2004.	Used alongside API CI-4, the designation CI-4 PLUS identifies oils formulated to provide greater protection against soot-related viscosity increase and viscosity loss due to shear in diesel engines. Like Energy Conserving, CI-4 PLUS appears in the lower portion of the API service symbol, known as the Donut.
CJ-4	Introduced in 2006 for high-speed, four-stroke engines.	Designed to meet 2007 on-road exhaust-emissions standards. Suitable for applications using diesel fuel containing up to 500 ppm (0.05% by weight) sulphur. Fuel containing more than 15 ppm sulphur may affect exhaust after-treatment system durability and/or oil-drain intervals. These oils help maintain emissions-control system durability when diesel particulate filters and other advanced after-treatment systems are used. CJ-4 oils exceed the performance criteria of CF-4, C-4, AH-4 and C-4 as written in the source.
CK-4	For high-speed, four-stroke diesel engines designed to meet 2017 model-year non-road exhaust-emissions standards, as well as earlier-model diesel engines.	Suitable for applications using diesel fuel containing up to 500 ppm (0.05% by weight) sulphur. However, fuel containing more than 15 ppm (0.0015% by weight) sulphur may affect exhaust after-treatment system durability and/or oil-drain intervals. Particularly effective at maintaining emissions-control system durability when particulate filters and other advanced after-treatment systems are used.

Additional information on API CK-4

API CK-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear and oil aeration. They also protect against catalyst poisoning, particulate-filter blockage, engine wear, piston deposits, deterioration 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. They can effectively lubricate engines requiring any of these API service categories.

When using CK-4 oil with fuel containing more than 15 ppm sulphur, consult the engine manufacturer for recommended service intervals.

1.3.3.2 CCMC: Committee of Common Market Automobile Constructors (Obsolete)

The CCMC classification system included the following categories:

• G (Gasoline) standard: G1 to G5 — petrol engines.
• PD (Passenger Diesel) standard: PD1 to PD2 — passenger-car diesel engines.
• D (Diesel) standard: D1 to D5 — commercial-vehicle diesel engines.

The letter identifies the type of standard, while the number indicates the performance level.

ACEA: European Automobile Manufacturers’ Association

ACEA standards progressively replaced the CCMC standards. The letter or number following each designation indicates the oil’s performance level. This level evolves as engine technology advances, including turbocharging, multi-valve designs and unleaded petrol engines.

A. CCMC Passenger-Car Diesel Engines

Standard	Application	Notes
PD1	Passenger-car diesel engines, with or without turbocharging.	Discontinued in 1989. The only standard of its type with specific test procedures for high-speed passenger-car diesel engines.
PD2	Passenger-car diesel engines, with or without turbocharging.	Replaced PD1 in 1989. Provides improved protection.

B. CCMC Commercial-Vehicle Diesel Engines

Standard	Application	Notes
D1	Naturally aspirated diesel engines.	Discontinued in 1989. API CC level plus specific European tests. Used until 1989.
D2	Naturally aspirated and supercharged diesel engines operating under heavy loads.	API CD / MIL-L-2104 D level plus specific European tests. Discontinued in 1989.
D3	Naturally aspirated and supercharged diesel engines operating under very heavy loads.	Discontinued in 1989. Performance level above API CD. Super High Performance Diesel (SHPD) oil for extended service intervals.
D4	Naturally aspirated and supercharged diesel engines operating under heavy loads.	Replaced D2 in 1989. Provides improved protection.
D5	Naturally aspirated and supercharged diesel engines operating under very heavy loads.	Replaced D3 in 1989. Provides improved protection. SHPD oils, suitable for extended oil-change intervals.

1.4 ACEA Specifications

The 1999 ACEA standards for engine oils comprised three different classes: one for petrol engines, one for light-duty diesel engines and one for heavy-duty diesel engines.

Each class is divided into several categories, which in turn represent different performance levels:

• Petrol engines: A1, A2 and A3.
• Light-duty diesel engines: B1, B2, B3 and B4.
• Heavy-duty diesel engines: E1, E2, E3 and E4.

The general applications of each standard are described below for information purposes only.

The specific applications for each standard are determined by the vehicle and engine manufacturers themselves, according to the requirements of their own vehicles and engines.

1.5.1 Description of Standards and Categories

ACEA category	Description and application
A1/B1	Lubricant intended for engines designed to use low-viscosity oil to improve fuel economy. HTHS viscosity between 2.9 and 3.5 mPa·s, with a low HTHS value. This type of oil may be unsuitable for certain engines; consult the vehicle’s maintenance manual.
A3/B3	Lubricant for general-purpose use in petrol or diesel engines with indirect injection. Oil-change intervals of 5,000 to 10,000 km are indicated in the source. These oils may be unsuitable for certain high-performance engines.
A3/B4	Lubricant with very good viscosity stability, intended for high-performance engines, including direct-injection engines.
A5/B5	A1/B1-type lubricant suitable for direct-injection engines, according to the source.
C1	Low-SAPS lubricant (low sulphated ash, phosphorus and sulphur content), suitable for vehicles equipped with a catalytic converter and a particulate filter. Low HTHS viscosity, stated as greater than 2.9 mPa·s in the source. Designed to improve fuel economy.
C2	Mid-SAPS lubricant, suitable for vehicles equipped with a catalytic converter and a particulate filter. Low HTHS viscosity, stated as greater than 2.9 mPa·s in the source. Designed to improve fuel economy. Associated with Fiat and PSA.
C3	Mid-SAPS lubricant, suitable for vehicles equipped with a catalytic converter and a particulate filter. HTHS viscosity stated as greater than 3.5 mPa·s in the source. Associated with Mercedes-Benz, BMW and GM.
C4	The source describes this as a Mid-SAPS lubricant suitable for vehicles equipped with a catalytic converter and a particulate filter. HTHS viscosity stated as greater than 3.5 mPa·s. Associated with Renault and Nissan.

C. Heavy-Duty Diesel Engines

ACEA category	Description and application
E1	General-purpose engine oil intended for naturally aspirated heavy-duty diesel engines, with normal oil-change intervals.
E2	Engine lubricant providing a defined level of performance in terms of piston cleanliness, bore polishing, wear, soot dispersancy and lubricant stability. Recommended for diesel engines meeting Euro 1 and Euro 2 emissions standards. May also be used for extended oil-change intervals, subject to the manufacturer’s recommendations.
E3	Oil offering excellent viscosity stability for high-performance engines, primarily those using indirect injection. Suitable for extended oil-change intervals as specified by the manufacturer, or for other demanding applications as determined by the engine manufacturer.
E4	Oil offering excellent viscosity stability and a defined level of performance in terms of piston cleanliness, bore polishing, wear, soot dispersancy and lubricant stability, compared with E3. Recommended for heavily loaded engines meeting Euro 1, Euro 2 and Euro 3 emissions standards. May also be used for extended oil-change intervals, subject to the manufacturer’s recommendations.
E5	Oil offering excellent viscosity stability and performance in terms of piston cleanliness and bore polishing. It also limits wear and turbocharger deposits and provides a high tolerance for soot. Recommended for heavily loaded heavy-duty diesel engines meeting Euro 1, Euro 2 and Euro 3 emissions standards. May also be used for extended oil-change intervals, subject to the manufacturer’s recommendations.
E6	Very high-performance oils suitable for engines meeting Euro 1, Euro 2, Euro 3 and Euro 4 emissions standards, operating under extremely severe conditions with very extended oil-change intervals. Suitable for engines equipped with EGR (exhaust gas recirculation), with or without a diesel particulate filter, and engines equipped with SCR (selective catalytic reduction) systems for reducing NOx emissions. E6 quality is particularly recommended for engines equipped with particulate filters and is designed for use with low-sulphur diesel fuel (maximum 50 ppm).
E7	High-performance oils suitable for engines meeting Euro 1, Euro 2, Euro 3 and Euro 4 emissions standards, operating under extremely severe conditions with very extended oil-change intervals. Suitable for engines without particulate filters and for most engines equipped with EGR or SCR systems for reducing NOx emissions.