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The Puzzling Rules of Interchange


ATIEL, the technical association of the European lubricants industry and the continents counterpart to the American Petroleum Institute, last year unveiled new guidelines for base oil interchange of Group III base stocks. This was good news for Europes engine oil blenders, who face a laundry list of costly tests when switching among base oils. It also brought renewed attention to this item in the formulators toolkit, and how its application differs between North America and Europe.

Base oil interchange, or BOI, is an essential part of the process by which engine oils are tested and qualified against various engine oil categories and specifications. The fact that there are so many base oils of various levels of refinement and composition makes it vital that a system be in place to assure finished engine oil quality, even when base oils change or become unavailable.

BOI was developed 20 years ago, early in the creation of APIs Engine Oil Licensing & Certification System, to accommodate the large number of base oils that were being used and to provide a rational system for exchanging one base oil for another in an approved product.

To simplify the interchange process, API developed its well-known base oil groupings, lumping together base oils of similar properties and allowing some systematic testing protocols to be developed. API still pigeonholes base oils according to their viscosity index, volatility and sulfur content, and ATIEL defines the groups identically for Europe (see Table 1, page 24).

Both organizations have written guidelines to ensure engine oil quality is maintained whenever a blender substitutes one base oil for another. Each allows a certain amount of base stock within a grouping to be commingled without further testing, which saves time and money for formulators. API guidelines are used around much of the world, while ATIELs are accepted as best practice for manufacturing engine oils conforming to Europes oil specifications, called ACEA Oil Sequences. (ACEA is the European Automobile Manufacturers Association.)

Of course, none of the base oils within a group are exactly the same. That means that even oils of the same group need some testing to assure that satisfactory performance is maintained when exchanged for another oil.

ATIEL, however, is far stricter about this than the API. Where API guidelines generally waive additional engine testing if the interchange is less than 30 percent or if viscometrics are appropriate, the ATIEL guidelines call for a barrage of tests whenever the interchange is greater than 10 percent.

One Fewer Test

ATIEL-required engine tests for satisfying ACEA Oil Sequences include the Peugeot TU5JP-L4 test for high-temperature deposits; Sequence VG (low-temperature sludge); the DB M111 (black sludge) and M111 FE (fuel economy); Peugeot TU3MS (valvetrain scuffing wear); VW DV4TD (dispersivity); VW TDI (ring sticking and piston cleanliness); and DB OM646LA (wear).

Based on analysis of TU5JP-L4 Peugeot engine test results, ATIEL last summer determined that the number of engine tests needed to validate the use of alternative Group III base stocks from different suppliers can be somewhat reduced when formulating engine oils to meet the latest technical performance specifications. This represents a savings in testing time and cost.

ATIEL drew on its members existing TU5 test data and statistically analyzed 13 different data points, with six current base oil manufacturers and seven different additive packages. The data from all the submitted and acquired engine tests, including all combinations of base oil and additives packages, identified two major influences on TU5 performance: the additive chemistry and, more emphatically, the base oils Noack volatility.

Both factors can affect lubricant viscosity increases under high-temperature operation, which is one of the key parameters of the TU5 test, but 80 percent of the variance in test results could be attributed to Noack, Kuwait Petroleums Adri van de Ven, chairman of ATIELs Base Oil Interchange committee, said in an October statement.

He continued, Group III base oils have become an important element in automotive lubricants. They are one of the key base stock groups for meeting the latest specifications of European OEMs, as set out in the ACEA Oil Sequences.

Van de Ven noted that the Group III base oils must be manufactured in accordance with the ATIEL Code of Practice in order to be used in ACEA-qualified engine oils, adding, Only lubricants produced in accordance with the Code of Practice, a fundamental part of the European Engine Lubricants Quality Management System, can legitimately claim to meet the performance requirements of ACEA.

Notably, the revised interchange guideline does not remove the need for lubricant developers to run all the other engine tests prescribed by the ATIEL Code of Practice, just the TU5 – and only if the Noack volatility is lower for the interchange oil than for the original. This is a small victory, but even the elimination of the TU5 is good news since the test costs around 20,000 and has a pass/test ratio of only about 65 percent.

The Goal: Broad Coverage

As the TU5 example shows, BOI aims to allow multiple base oils to be approved with a specific additive system without running a complete engine test approval program for each base oil combination, provided there are data to support it. Depending on what sort of base oil exchange is being proposed, certain tests are required to demonstrate equivalent performance. One or more of the engine sequence tests required for original category approval must be run, but the obvious goal is to minimize testing costs and gain the broadest coverage in base oils.

One test that is practically a given when switching between base oils is the Sequence IIIG, which among other things measures the oxidation resistance of a formulation. Base oil manufacturers insist on this test as a means of assuring that their product is not being replaced by another which doesnt meet the standards established. (Not surprisingly, there have been instances where a base oil from an equivalent group doesnt perform as well as the base oil it is replacing.)

There are a number of other engine tests which might be influenced by base oil selection. For many of these, oxidation stability, while not the primary criterion, seems to play a part in the oils performance, according to sources at additive companies. In addition, deposit formation is influenced by the molecular structure of the base oil. Physical and chemical properties such as sulfur content and volatility also play a part.

ATIELs most recent update changed its Group III BOI guidelines to eliminate one test under specific conditions. Yet, ATIEL and API remain far apart on Group III-to-Group III interchanges. (See Table 2.)

Whos in Charge?

The primary reason for the difference is that the European approval system is driven by OEM requirements and approvals, while the API system is managed by oil companies. Through ACEA, Europes automakers control the engine oil categories for the continents vehicles. Its Oil Sequences, denoted by a series of letters such as A1/B1-10, are subordinate to European OEM approvals.

Additionally, if a product achieves a blanket approval (usually three separate programs) on an OEMs lubricant specification (such as Daimler-Benzs), then ACEA approval is assumed without further testing.

When Group III-to-Group III interchange testing is required by API guidelines (remember, greater than 30 percent) engine testing can stop after doing the Sequence III and Sequence V, provided certain viscometric targets are met. Given the cost of engine testing, you can bet that the viscometrics will be met!

The focus in this article has been on Group III-to-Group III BOI. However, other interchanges should not be overlooked, including exchanges between groups. Interchanges between Group II and Group I base stocks may be made, for example, and each proposed switch has its own set of testing rules.

As a general rule of thumb, its useful to know that replacing a lower-numbered base oil group with a higher-numbered group often requires less testing than the reverse. This is especially apparent in heavy-duty diesel engine oils, where Group II base oils provide much better performance than Group I base oils in tests where soot generation is crucial.

APIs complete rules for base oil interchange are found in Appendix E of API 1509, the Engine Oil Licensing and Certification System. Since Appendix E is edited and modified on a regular basis, formulators should always check for the latest edition at the API website at pubs/index.cfm.

For the rules on base oil interchange for ATIEL (originally the Association Technique de LIndustrie Europeenne des Lubrifiants), see Appendix B of its Code of Practice, which is kept updated at

BOI has been an important part of the engine oil approval process for nearly 20 years. It has resulted in broader base oil coverage for a particular additive system at a reasonable cost to the oil marketer and ultimately, the consumer.

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