BOI protocols were introduced as a response to finished lubricant field problems in the mid-1990s. Before then, the implicit assumption had been that it mattered little which base oils were used. In some ways, this is becoming more true today – a fact recognized by API (the United States-based American Petroleum Institute) in its current BOI guidelines for more recent service categories. But that certainly was not the case when the first protocols were introduced.

There definitely were some historic quality issues stemming from the practice of using a high quality base stock slate to qualify an additive technology and then switching to lower quality base stocks during production. In the 90s, there was also much greater use of API Group I base stocks, which inherently had – and still have – a greater range of chemical compositions and performance. Finally, base stock effects on finished lubricant performance were much less understood then.

Before BOI, there were no restrictions on substitution of base stocks from different manufacturers in combination with a given additive package. API SH and earlier specifications for oils used in vehicles with spark ignition, as well as API CD and earlier specs for heavy-duty diesel engine oils, were not subject to BOI. Its worth noting that those older categories had much lower additive treats, which amplified base oil impacts.

API and ATIEL (the Technical Association of the European Lubricants Industry, headquartered in Brussels) take similar approaches to BOI protocols. In essence, a BOI program is the rerunning of a product qualification program with reduced requirements for engine tests; only those engine tests that have a demonstrated base oil appetite must be repeated. This saves costs compared to repetition of all engine tests. However, if there is no data to support waiving an engine test when changing base stock slates, then by default the engine test is run under both API and ATIEL approaches. This is why there may appear to be excessive constraints on interchanging base stock slates. Its not necessarily that there is a technical reason that an engine test needs to be repeated; it is just that there is a lack of data to show that it does not need to be repeated.

API gives some relief to running standard BOI programs through the Single Technology Matrix, where a book-end approach to base oil compositions allows specific additive packages to be qualified with multiple base stock slates. However, this requires a significant upfront investment in cash and R&D effort, and thus is only cost-effective where base oils from large numbers of sources need qualifying with one additive technology. ATIEL similarly gives some relief though its Slate Linking approach. Again, a significant upfront investment is required. Such approaches will only be appropriate to additive companies or finished lubricant blenders that have global reach causing them to use many slates.

OEMs generally dont allow BOI for factory fill products. This is understandable for vehicles still in warrantee. Although there is some base stock interchange allowed for service fill products, even these interchanges are attracting more rigor as both European and U.S. OEMs publish specific aftermarket requirements.

Is it time to revisit how BOI is allowed? Over the years, the industry has certainly seen narrowing of the bandwidth in terms of base stock compositions amongst Group II and Group III slates which can be investigated, with the balance of iso-paraffin versus naphthenic molecules replacing sulfur and aromatics content for main consideration.

Almost all new base stock projects are Group II or III, and since the vast majority of new base stocks are produced using the licensed technology from around three main global technology suppliers, can there be that much difference in chemistry and performance for the bulk of existing and new base stock supplies?

Moreover, as the top-tier products of today trickle down to become the mainstream products of tomorrow – a shift accompanied by higher additive package treat rates and hence greater base stock slate resilience – we may find we come full-circle to a point where BOI becomes very much simpler and base stocks become more readily fungible. If this does occur though, the difference this time will be that it comes about because we do actually understand much better whether there are significant base stock effects on crankcase lubricant performance, rather than just assuming base stock effects were not important until we saw field problems, as was the case a couple of decades ago.