Base oil groups are defined identically by API and ATIEL, according to their viscosity index, volatility and sulfur content. Both organizations have written guidelines to ensure engine oil quality is maintained whenever a blender substitutes one base oil for another. Each allows base stocks within an approved group to be commingled without further testing, which saves time and money for formulators.

ATIEL Group III-to-Group III interchange, however, differs from the API version. Where API Appendix E guidelines generally don’t require testing if the interchange is less than 30 percent or if viscometrics are appropriate, the ATIEL guidelines call for a barrage of tests if the interchange is greater than 10 percent.

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

Based now on analysis of TU5JP-L4 Peugeot engine test results, ATIEL has determined that this test can be safely skipped when formulators use alternative Group III base stocks from different suppliers — provided that the alternative Group IIIs volatility is the same as or lower than the original. This represents a savings in testing time and cost, without invalidating the technical performance of the finished engine oil, ATIEL found.

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 the submitted and acquired engine tests, including all combinations of base oil and additives packages, identified Noack volatility and additive chemistry as the two major influences on TU5 performance.

“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 [volatility],” commented Adri van de Ven, chairman of ATIEL’s Base Oil Interchange committee.

Van de Ven 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 (Association of European Automotive Manufacturers) Oil Sequences.”

He 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. According to Van de Ven, “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.”

ACEA sequences are increasingly driven by emissions legislation which means lubricant producers must use higher quality base stocks in order to meet more stringent emissions limits — resulting in the use of more Group III base oils. The growth in Group III demand has encouraged significant investments in new base oil capacity, raising concerns that these base oils may vary significantly according to the individual producer, refinery or blending process employed. By establishing strong interchange guidelines, ATIEL believes this will provide assurance that finished lubricants will meet all requirements.

The revised interchange guideline does not remove the need for lubricant developers to run other types of engine tests prescribed by the ATIEL Code of Practice. The Group III base oil interchange guideline, covering the ACEA A/B and C Sequences, has been incorporated into Appendix B of the ATIEL Code of Practice, available online at http://www.atiel.org/codeprac.htm.