Oil Service Classifications

Hannu Jääskeläinen

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Abstract: A number of oil specifications have been developed to ensure that lubricants provide all of the lubricating oil functions required in modern engines. In the USA, the API oil classification system provides a simple designation for engine oils to ensure that the proper type of oil is selected for an engine. Oil classification systems have been also in place in the EU and Japan.

API Classifications

API Oil Service Categories

The API Engine Oil Licensing and Certification System provides a simple designation of letters and numbers that allows engine manufacturers and oil marketers to clearly provide users with the information they need to ensure that the proper oil is selected for an engine. Each letter/number designation identifies a service category (e.g., CI-4) which is linked to a series of tests that the oil must pass before it is allowed to carry that designation. The API “S” series describes oil standards primarily for gasoline engines while the API “C” series describes oil standards for diesel engine service. A description of the API service symbol and category mark can be found in the Engine Oil Guide published by the API [1875].

Table 1 outlines some API “C” series service categories and the general performance requirements that the oil must meet. From time-to-time, engine manufacturers may issue additional requirements if there is not a current API classification that meets their needs. Table 1 also provides information on the minimum backward compatibility of specific categories. While newer service category oils generally provide backward compatibility to older service categories, they may not be compatible with all older categories. For example, service category CI-4 is not required to be compatible with service categories CF or CF-2. Individual oils may however be designed to provide additional compatibility to those outlined in Table 1. By 2012, all service categories except CH-4, CI-4 and CJ-4 were obsolete and a new one was under development. A common reason for the obsolescence of the older categories is a lack or facilities and parts to run some of the key engine tests.

Table 1
API oil service categories

CategoryYear of IntroductionEngine Service DescriptionBackward Compatibility
CF1994

Intended for off-road engines which use fuel containing more than 0.5% sulfur. Provides control of:

  • piston deposits
  • piston, ring and liner scuffing
  • wear and corrosion of copper containing bearings

This service category was discontinued on December 30, 2010.

CD
CF-21994

Intended for 2-stroke diesel engines. Provides control of:

  • piston deposits
  • cylinder and ring-face scuffing
  • wear and corrosion of copper containing bearings

This service category was discontinued on August 31, 2009.

CD-II
Does not necessarily meet the requirements of CF or CF-4 oils.
CF-41991

Intended for high speed, 4-stroke, on-highway heavy-duty diesel engines meeting 1991 emission standards. Provides control of:

  • piston deposits
  • piston, ring and liner scuffing
  • corrosion and wear of copper containing bearings
  • oil consumption
  • ring and liner wear
  • oil thickening due to soot

This service category was discontinued on June 30, 2008.

CD and CE
CG-41995

Intended for high speed, 4-stroke diesels used in on- and off-highway applications and using fuels with less than 0.5% sulfur. Especially for engines meeting 1994 emission standards.

In addition to providing control of the parameters listed for CF-4 oils, the classification provides additional control of:

  • oil filter plugging due to soot
  • oil thickening due to oxidation
  • valve train wear
  • foaming

This service category was discontinued on August 31, 2009.

CD, CE and CF-4
CH-41998

Intended for high speed 4-stroke diesels meeting 1998 US EPA emission standards and using fuels with less than 0.5% sulfur.

In addition to providing control of the parameters listed for CG-4 oils, the classification provides additional control of:

  • viscosity loss due to shear
  • sludge
  • oil volatility
CD, CE, CF-4 and CG-4
CI-42002 Intended for high speed 4-stroke diesel engines meeting 2004 US EPA on-highway emission standards implemented in 2002. Formulated to sustain engine durability where EGR is used. Intended for use with fuels having less than 0.5% sulfur.

In addition to providing control of the parameters listed for CH-4 oils, the classification provides additional control of:

  • low temperature pumpability
  • elastomer compatibility
  • high-temperature/high-shear viscosity
CD, CE, CF-4, CG-4 and CH-4
CI-4 Plus2004

Meets all requirements of CI-4 but includes increased resistance to oil thickening from soot and increased shear stability.

CD, CE, CF-4, CG-4 and CH-4
CJ-42006

Intended for high speed 4-stroke diesel engines meeting 2007 US EPA on-highway emission standards.

In addition to providing control of the parameters listed for CI-4 oils, the classification provides additional control of:

  • sulfated ash, phosphorous and sulfur content
CI-4 and CI-4 Plus
CK-42017

Intended for high speed 4-stroke diesel engines meeting 2007 US EPA on-highway emission standards.

In addition to providing control of the parameters listed for CJ-4 oils, the classification provides additional control of:

  • engine oil aeration
  • engine oil oxidation
  • viscosity loss due to shear
CJ-4
FA-42017

Intended for some high speed 4-stroke diesel engines meeting 2017 US EPA on-highway emission standards. This classification provides the same benefits as CK-4 oils but is also intended to enable fuel economy benefits for heavy-duty engines by introducing oils with lower high temperature/high shear viscosity than CK-4 oils.

none

Additional details on API classifications and testing are discussed under API Oil Service Categories.

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