Both API and ATIEL systems have global reach, between them covering all major crankcase lubricant specification systems, including API, ILSAC/JASO and ACEA. Since their adoption, there has been little modification to the original base oil group structure or definitions, apart from a short-lived excursion by ATIEL to accommodate polyinternal olefins from a single manufacturer as ATIEL Group VI. These PIOs had certain interchangeability with Group IV, but API never adopted them. Group VI no longer exists even within the ATIEL Code of Practice.

Opinions vary regarding whether changes should be made to the groups. Regardless of what happens, the effective equivalence of API and ATIEL group definitions must remain to simplify development and interchange testing for a product carrying both API and ACEA claims. This is especially true because several API engine tests have been adopted by ACEA, particularly for heavy-duty diesel engine categories.

My opinion is to maintain the status quo, mainly because any changes involving greater granularity in base stock definitions would almost certainly add more complexity and cost to product qualifications and base oil interchange, likely decreasing the potential for straightforward interchange. This runs counter to opinions expressed in several recent presentations, particularly from additive suppliers, to simplify the crankcase lubricant qualification process.

No compelling issues, such as field problems, have been cited that can be laid at the feet of the current base oil groupings and associated BOI. To be sure, some things occur that should not – such as base stock manufacturers letting typical properties slip compared to their historic values, while remaining formally within the group specification windows.

However, this situation cannot be corrected just by tightening group specification windows. Otherwise, the system ceases to provide purely broad base stock definitions, as originally intended. Rather, it would become a manufacturing tolerance policeman, which it was never intended to be. It is up to procurement personnel at lubricant blenders to negotiate suitable typical property windows to accommodate genuine and unavoidable manufacturing variability.

Almost as soon as the official API groups were adopted, unofficial Group II+ appeared, with a viscosity index near 119 rather than the more typical 100. This allowed for the light grade Noack correctors to be included in a single interchangeable Group II slate, rather than straying into what was always more constrained Group III territory. BOI between Group II slates, including Group II+, is subject only to the far less constraining Group II to Group II rules.

Looking closer at Group II slates, any Group II+ Noack corrector would normally have a separate product name or code, compared to a higher Noack grade with the same kinematic viscosity. The ATIEL code of practice states explicitly, The lubricant manufacturer shall ensure that the formulation used for the commercial product accurately reflects the formulation used to establish the ACEA Performance Data Set. This includes in particular the choice of raw materials. API 1509 Appendix E uses similar wording.

As a result, blenders are precluded from using a Group II+ in product development as well as from substituting a regular Group II of the same slate in commercial blending. Therefore, based on this example, there is no need to unduly differentiate Group II and Group II+ by recasting the group structure, provided Group II stocks are used in a compliant manner in both product development and commercial blends.

It should be said that Group II+ was sometimes a reflection of a manufacturers inability to robustly or economically make Group III, rather than to avoid Group III interchange complications. This could be due to feedstock or refining constraints. Group II+ was the best they could manage to produce in raising VI, which is a necessary step in making a low-volatility grade, since high VI correlates with higher boiling components.

The industry also ended up with a complementary, and equally unofficial, Group III+ class for stocks with VI greater than 130. This seems to be purely a marketing issue because there is no BOI or other advantage to be achieved within Group III.

Any narrowing of the current base oil group specifications would make it necessary to ensure that they did not close in on reasonable and realistic manufacturing tolerances. Also, any new specifications would need to be truly independent variables and not coupled with some other specification. For example, VI and Noack can be weakly coupled functions.

Therefore, if we do ever see any changes to base oil group definitions, we need to avoid unintended consequences to ensure that the current reasonably effective system is not replaced with more complexity and cost, on top of an already over-complex lube product development and BOI system.