Arecent study by the Automobile Association of America found synthetic engine oils performed significantly better, by 47 percent, than conventional (mineral-based) engine oils, using a range of industry standard tests. It would have been a bit disappointing if the conclusions had been anything else.

Without seeing exactly how the study was structured, one thing that immediately springs to mind is there are generally more differences between synthetics and mineral-based crankcase lubricants than just the base oil.

Most lube blenders tier their product range, sometimes to quite significant levels of differentiation. This means that the finished lubes will have an associated tiering of additive treat rates, with the top tiers having the highest treats. This can also be finessed with so-called top treats, where the basic additive package technology stays the same – so full product development does not need repeating – but some differentiating attribute of cleanliness or fuel economy, etc., is achieved through permitted minor modification additive boosts being applied.

All this is in addition to the change in base stock group, as one goes up or down the tiers, with heavier-grade, mineral-based mainstream base oil products used towards the bottom tiers (API Group II and some Group I) and synthetic (Group III or IV) towards the top tiers.

Therefore, it can be fairly difficult to pick out the specific effect of the bulk additive treat rate or top-treat from the contribution of the base stock. Identifying the effects of the base stock alone would require a large and expensive research and development matrix of, probably, non-commercial oils, in order that one variable (base stock or additive treat) can be examined at time.

This does not detract from the AAAs findings that synthetic lubricants perform better, which is undoubtedly correct. But it is important to draw the right conclusions that it is the overall finished lubricant that delivers the superior performance – enabled by both quality synthetic base stocks and relatively higher additive package treats – rather than just the base stock itself. As previously written in this column, it is possible to put together a synthetic lubricant that would have woeful performance compared with a mineral finished lubricant.

Synthetics, or Group III and Group IV-based lubricants, are technical requirements for the low-viscosity, very low Noack finished lubricants found in both passenger car and heavy-duty diesel engines. In fact, some of the higher-performance European Automobile Manufacturers Association heavy-duty diesel engine oil categories have positively required the Group III or IV synthetic approach for quite a while.

Among industrial lubricants, we also see now similar tiering approaches. Industrial lubricants are associated with quite low additive treat rates for necessary technical reasons. Hence, synthetic base stocks often show even greater relative benefits over mineral base stocks in industrial lubes than in the crankcase arena. This is because of improved base oil additive responses at low additive treat rates with Group III and IV, where the effects of base oil quality are not swamped by very high additive treats.

In fact, use of light-treat industrial lubricants as a differentiator of base stocks inherent quality is, perhaps, the best way of demonstrating compositional superiority both between synthetics and mineral base stocks and also within any given API group.

Data gathered by Kline & Co. has shown the largest percentage global demand growth for passenger car motor oils between now and either 2020 or 2025 will be SAE 0W-XX grades, which must, of course, be based on synthetic stocks. The largest percentage shift in the global HDEO crankcase market over the same time periods will be in the SAE 10W-XX grades, and these can be currently formulated with higher viscosity index Group II (i.e., Group II+) base stocks, which are not conventionally regarded as synthetic, even though there is no significant difference in feedstocks or processing.

SAE 10W-XX oils can also be formulated with Group III or IV, but I doubt whether most truck operators really care about synthetic claims, relying instead on original equipment manufacturer approvals for their choice of service-fill lubricants.

We are still in the position that there is no formal lubricants industry body definition of what constitutes a synthetic base stock or synthetic lubricant. We have just the informal acceptance that lubricants containing Group III or IV are the only hydrocarbon base oils to constitute full synthetic lubricants. So there must be an element of buyer beware about this unregulated synthetics area, especially when getting into even less defined realms of semi- or part-synthetic.

It is telling that no lubricant industry body wants to get involved in such a technical definition process, since synthetic claims are simply marketing claims. However, since the use of the synthetic claim is so widespread, some efforts should be made, either by educating the consumer or dropping the term altogether. Having been asked many times the synthetic question, I would opt for dropping the term and just concentrating on performance.