1.4.1 Introduction
In the early years of automobile use, engine oil had to be added or changed after an exceedingly brief interval. In addition, oils were not standardized. Individual vehicle operators could be at the mercy of their intuition with regard to the purchase of an appropriate automotive lubricant for their cars. With time, people began to realize that something had to be done to avoid the possibility of serious adverse consequences if a driver had used the wrong kind of oil for an engine. Thus, there was strong motivation to look for chemical agents that both provided protection to an engine and promoted long life of the engine oil. This trend (toward improving engine and oil durability and using additives in the oil to provide specific beneficial attributes) is ongoing. Promoting environmental acceptability has also become an essential ingredient of responsible engine oil formulation. Throughout these developments, it has been essential to create and conduct appropriate engine oil test methods that ensure oils available to the public produce appropriate engine protection.
Various classes of standard tests are available to confirm that current automotive engine oils provide the desired protection, including long oil life, corrosion and wear protection, resistance to the formation of
sludge and deposits, ability to remain within an appropriate viscosity range, etc. ILSAC (the International Lubricant Standardization and Approval Committee) and API (the American Petroleum Institute) are two organizations that play a major role in overseeing the availability of standard engine-oil-related test methods. The American Society for Testing and Materials (ASTM) is typical of the organizations that publish standard procedures to be used when conducting an automotive test. Such standard tests are prepared in painstaking detail, so that there will essentially be no chance of conducting a standard test incorrectly if one has followed the written directions. Automotive companies tend to be the developers of such tests. In general, different tests are used for gasoline-fueled engines than are used for diesel engines.
Tests typically need to be updated periodically, for various reasons. In some cases, test components, such as a specific type of engine, may no longer be available. Changes in the chemical nature of the fuel, such as the transition from leaded to unleaded fuel, may mean that a former test is no longer pertinent to current engine wear, corrosion, and sludge characteristics. Future engine designs that differ from current test engines mean that standard tests will have to be created using the newer types of engines, since the older engines may not be predictive of current performance. If it is possible to legitimately substitute a bench test for an engine test (such that the fundamental mechanisms of oil and engine damage correlate strongly with the results from the bench test), the bench test becomes far less labor intensive and expensive.
A brief overview of the evolution of standard engine oil test methods and the status of current automotive engine oil test method development is provided in the following paragraphs.
Early test methods for engine oils were far less sophisticated and less specialized than the tests of today.
It can be anticipated that the tests of the future will be even more specialized. Wherever possible, bench tests will be substituted for engine dynamometer tests, such as was the case in the development of the Ball Rust Test, a bench test that replaced the Sequence IID (i.e., Sequence 2D) engine test, which measured the ability of an engine oil to protect against the kind of corrosive damage that can occur during extended short-trip winter service in which water and corrosive chemicals (derived from the partial combustion of the fuel) enter and remain in the engine oil for extended periods and cause engine corrosion.
At the fundamental level, oil analyses can determine whether a given engine oil has all the required additives in its formulation (and thus is not deficient, such as an “SA” quality oil would be). Such inform- ation can be pertinent to engine durability field problems, since most vehicle warranties are invalidated if the wrong grade of engine oil has been used in an engine.
As of early 2004, the only two designations widely used to describe light-duty, gasoline engine oil performance were API SL and ILSAC GF-3. Later in 2004, API SM and ILSAC GF-4 oils became available in the marketplace. The engine test and bench test performance requirements for API SL are similar to those for ILSAC GF-3, but, in addition, ILSAC GF-3 oils must also meet energy conserving requirements.
Similarly, API SM requirements as well as energy conserving requirements must be passed before an engine oil can be designated as ILSAC GF-4.
The test methods for engine oils must be in accordance with the requirements outlined in the American Chemistry Council (ACC) Product Approval Code of Practice. These requirements include registration of all tests, use of only calibrated equipment and facilities, and guidelines for acceptable modifications during program development. These requirements were implemented when the API SH and ILSAC GF-1 designations for engine oil were adopted in 1993, and the requirements have been continued as new performance categories have evolved.
1.4.2 ILSAC GF-4 and API SM Standard Tests
In January 2004, ILSAC issued its latest Minimum Performance Standard for Engine Oils, ILSAC GF-4.
Compared with GF-3 (the previous engine oil category), oils meeting GF-4 requirements provide improved oxidation resistance, improved high-temperature deposit control, better cam and lifter wear discrimina- tion, improved low-temperature wear protection, and improved low-temperature used-oil pumpability.
ILSAC GF-4 oils also have reduced phosphorus and sulfur contents to provide enhanced emissions system protection and to help vehicles meet the stringent Tier 2 Bin 5 emissions standards, which require, among other things, that vehicles emit no more than 0.07 g/miles (0.045 g/km) of nitrogen oxides over
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120,000 miles (190,000 km) of driving. GF-4 oils also provide improved fuel efficiency for both new and used oils, compared with GF-3 oils. GF-4 oils began to be marketed during the second half of 2004, and all oils licensed to display the API Certification Mark (starburst) must meet GF-4 requirements by April 30, 2005.
The companion S category to GF-4 engine oils, designated API SM, was defined by the API Lubricants Committee. The API SM category includes the same performance requirements (except for fuel efficiency) as ILSAC GF-4, for those viscosity grades defined by GF-4 (i.e., SAE 0W-20, SAE 5W-20, SAE 5W-30, and SAE 10W-30). For other non-ILSAC viscosity grades, some other differences between API SM and ILSAC GF-4 requirements exist, as outlined in API 1509, “Engine Oil Licensing and Certification System,” latest edition. Descriptions of the standard tests for ILSAC GF-4 and API SM engine oils follow.
Although the performance limits in many of the engine and bench tests in ILSAC GF-4, as well as the chemical compositional requirements, were modified to achieve the benefits described previously, there was only one new engine performance test developed for GF-4 (the Sequence IIIG Test, which replaced the Sequence IIIF Test, ASTM D 6984). The IIIG Test utilizes the same General Motors 3800 Series II engine used in the IIIF Test, but the IIIG Test has different operating conditions and uses retrofitted valve train metallurgy. The measured parameters in the IIIG Test include average cam plus lifter wear, end-of-test kinematic viscosity increase, and a composite assessment of piston deposits. An end-of-test oil sample from the IIIG Test is also evaluated for its low-temperature engine oil pumpability characteristics (ASTM D 4684). In addition, the test length was increased to 100 h (from 80 h in the IIIF Test), engine load was increased from 200 to 250 Nm, and sampling and additions of make-up oil were minimized to increase the severity of the IIIG Test. Oil sump temperature was actually decreased from 155 to 150◦C in IIIG (a decrease in test severity), because of concerns over abnormal depletion (degradation) of the engine oil’s antioxidant/antiwear agent, ZDP, at temperatures above 150◦C. The Sequence IIIG Test retains the same alloy-cast-iron lifters used in the IIIF Test, but in the Sequence IIIG Test, the camshaft is phosphated (with a manganese phosphate coating) to minimize scuffing during break-in of the test engines. Thus, the Sequence IIIG Test addresses the issues that were of concern at the time of its inception. As conditions and issues evolve, it can be anticipated that this test (and other test methods) will evolve to meet future needs.
The Sequence IVA (i.e., 4A) Test mimics city service and determines whether the engine oil provides sufficient wear protection to an overhead cam and slider followers. The Sequence VIII (i.e., 8) Test measures the extent of shear of the viscosity index improver. In addition, the Sequence VIII Test determines whether the engine oil provides sufficient protection to copper-lead bearings when using unleaded fuel. The previously available test (L-38) used leaded fuel, and thus the L-38 test is no longer appropriate for vehicles using the current unleaded fuels. The Sequence VG Test (i.e., 5G) addresses some of the issues related to partial replacement for the Sequence VE Test (ASTM D 5302). Sequence VG measures the sludge and deposit control tendency of engine oils under engine conditions that simulate stop-and-go city service in vehicles.
The Sequence VIB (i.e., 6B) Test replaces the Sequence VIA Test (ASTM D 6202) for measuring the fuel- efficient properties of an engine oil. Like its predecessor, the Sequence VIB Test measures the improvement in fuel efficiency of a test oil compared with an ASTM standard reference oil. Unlike its predecessor, however, the Sequence VIB Test not only measures the fuel efficiency of the oil when it is relatively new (after only 16 h of aging in the engine), but also the fuel efficiency after 96 h of aging, which corresponds to about 4000 to 5000 miles (6400 to 8000 km) of vehicle operation. Different levels of fuel efficiency improvement are required, depending upon the SAE viscosity grade of the engine oil (the same groupings of viscosity grade as were defined in the ILSAC GF-2 requirements for the Sequence VIA Test). Sequence VIB fuel efficiency requirements apply only to ILSAC GF-3 and GF-4 oils, not to API SL or SM oils.
The Ball Rust Test is a bench test that mimics the effects of extreme short-trip winter driving. It replaced a previously used engine dynamometer test, and thereby saves considerable expense, time, and effort in the testing process. In the test, an engine component (ball) is immersed in a fluid that contains engine oil to which has been added the kinds of corrosive chemicals that are generated from incomplete combustion of the fuel when the oil and the engine are very cold (e.g., organic acids and other oxidized compounds).
At the end of the test the extent of rust formation is evaluated electronically.
As can be seen, test methods for engine oils can be complex, time consuming to develop, and expensive to run, and they need to be revised whenever engine designs have changed (e.g., as a consequence of environmental issues, including modifications to fuels, lubricants, or engine materials). Thus, the upgrading of standard tests is an essential and ongoing effort to ensure that new materials, engine design, fuels, and government mandates related to vehicle operation are adequately addressed.