For those of you who havent seen it, the table below is a summary of the five American Petroleum Institute base oil groups. Youll note that only the first three groups are defined by physical and chemical properties.

Ernie Henderson, one of the gurus who created the base oil classification system, pointed out that the original driver behind this was engine oils.In the 1990s, engine oils were formulated with paraffinic base oils, so API groupings were associated with paraffinic base oils. Polyalphaolefin was added in response to the creation of high viscosity index paraffinic Group III base oils, and everything else was deferred to Group V.

Base oil interchange is closely tied to the base oil category system. Certain properties such as saturates, V.I. and sulfur content play a major role in determining what testing is needed to verify lubricant performance when the base oil is swapped out in a formulation.

Stefan Muller of IHS Markit in Switzerland wrote seeking clarification on the base oil category system found in API 1509. His question was why naphthenics are lumped into Group V along with some synthetics, polyglycols and several other miscellaneous lubricating oils.

Muller questioned the system, saying that a set of physical and chemical parameters enabling base stock exchanges or qualification for certain applications should not be covered by a badly defined set of chemical structures. As an example, he offered a set of data on a Nynas naphthenic oil that meets API Group II requirements but would be categorized as a Group V.

He feels that the correlation between physical and chemical criteria and structure in such a broad fashion is not a good idea. Instead, Muller proposed the arrangement on page 8.

BOI and VGRA

This is one of the most important parts of API 1509, which is the roadmap for automotive engine oil testing. It is used by engine builders, oil marketers and petroleum additive suppliers to develop and commercialize engine lubricants. Henderson notes that base oil interchange and viscosity grade read-across were the driving forces for the base oil classification system.

Broadly speaking, BOI and VGRA were developed to mitigate the cost of engine testing. Ive mentioned on several occasions that a complete engine test program for the new ILSAC GF-6 passenger car engine oil specification requires ten engine tests to meet category requirements. These tests are not cheap! If a test program meets all ten on the first run, you would still be spending over half a million. Unfortunately, the statistics arent that good. You can almost count on one or more tests missing on some parameter, which means the cost goes up.

BOI allows you to take a completed engine test program and, by making some base oil adjustments, run some but not all tests to approve the formulation with a different base stock.

VGRA works on a similar principle, only now youre looking at different viscosity grades. By selecting the most difficult viscosity grade to run in each engine test, you can get broad coverage with fewer tests. Both of these guidelines are a valuable part of the engine oil development and approval processes.

One of my regular correspondents, Blaine Ballentine in Iowa, raised a question regarding what seemed to him to be a counter-intuitive interpretation of BOI and VGRA rules. Specifically, he referenced BOI guidelines for the Sequence IVB wear test, which essentially says that a successful Sequence IVB result in a Group II formulation covers all Group II and Group III based formulations, provided the base oil viscosity at 100 degrees Celsius is equal to or greater than the tested oil. However, Ballentine noted that Group IV appears to require that Sequence IVB tests be run.

Why, he asked, did Groups II and III get what is essentially a free ride while PAO, which is supposed to be superior in every way, did not?

In fact, PAOs can be substituted, essentially test-free, if they meet the physical and chemical properties of the original tested product. Key properties include kinematic viscosity at 100 C, 40 C and minus 40 C; viscosity index; Noack volatility; pour point and saturates levels. The concern and reason for potential testing is that there will be subtle differences in the PAO blend used. The Sequence IVB is a new test and seems to be much more sensitive than its predecessor, the Sequence IVA, which only adds to the confusion.

Engine Oil Labeling

This is always a topic of great interest. API 1509 describes the technical designations required for any oil licensed by API. Beyond that, each oil marketer chooses its superlative language and supporting data that it hopes will make its product stand out.

Albert Frediani in Massachusetts, another regular, wrote to discuss engine oil labeling and especially how to differentiate between good, better and best oils. In my response, I shared some of the background on this advertising tool and offered some well-known examples like GMs main automobile brands: Chevrolet, Buick and Cadillac; and Anheuser-Buschs beer: Busch, Budweiser and Michelob.

Motor oil is no different.Many studies show that about 5 percent of motor oil consumers want the very best.Another group of early adopters wants to see the new categories and buys oil from a limited number of brands.Another group is very late to adopt new technology and doesnt care about brand, but wants it cheap.

Additive chemistry can also be used to claim differentiation.High mileage oils are a good example. They are standard additive systems that have additional seal conditioning and antioxidants added to help an engine run longer.Engine design is much better than it was 50 years ago when any engine lasting over about 75,000 miles was probably done.Now engines can last over 200,000 miles with no special maintenance required.

There is a clear legal decision (Pennzoil vs. Castrol) that says an advertiser cannot claim superiority on the basis of non-standard tests. Another case was decided by an advertising court: The National Advertising Division, associated with the Better Business Bureau, decided that severely refined base oils could be called synthetic since it was possible to produce equivalent oils either by refining or by synthesizing. Castrol, and later the entire industry, benefited from this decision. Bottom line: Get used to good-better-best, because it is not going away.

Motor Oil Viscometrics

I got a note from Don Johnson in Kansas (not the former VP of Pennzoil) regarding motor oil labeling and viscometrics. His question was how three different brands of SAE 0W-40 engine oil with widely varying viscosity data can be considered equivalent.

To answer this question, I reviewed SAE J300, the grandfather of all oil specifications. Each viscosity grade has a range of values. For example, at 100 C, SAE 40 has a viscosity range of 12.5 to 16.3 centistokes. In addition, there is a minimum high-temperature high-shear viscosity requirement of 3.5 centipoise if the winter grade is an SAE 0W. There are also low-temperature requirements to assure engine cranking and pumpability at startup. So long as all three oils stay within these boundaries, they are considered to be technically equivalent as far as viscometrics are concerned.

Given the viscosity grade (SAE 0W-40), its pretty likely that each base oil blend contains a significant portion of synthetic base stocks and a robust additive system to achieve the performance requirements of the API category.

Ken Budinski of New York wrote to ask about ILSAC GF-6 and how it fits into the engine oil story. He was also interested in the frictional properties of a lubricated system, noting that he believed oil did not have a coefficient of friction in and of itself. Ken also commented that he believes that we need to identifygenerally agreed upon teststo quantify frictional differences between oils.

This led me to a description of the API and ILSAC GF oil labeling system. I pointed out that the GF system as defined in API 1509 and in response to original equipment manufacturer requests is designed to give anyone purchasing oil for their vehicle a quick guide to purchasing the right oil. Any oil that has the ILSAC Starburst on the label is suitable for any engine. The only other criterion needed is the viscosity grade. It incorporates the latest API category as well as fuel economy performance.

ILSAC GF-6, the latest in the line, will be available beginning on May 1, 2020. API will not allow oil marketers to make the claim in any print or broadcast media until that date. I expect that prior to May of 2020, there will be many oils with the Starburst that meet the requirements for GF-6.

There are many challenges inherent in changing to a new performance level. Some of them are advertising and labeling re-designs as well as the logistics of changing additive systems. If the plant operations can be converted early, the label, advertising and marketing literature can be prepared for introduction on day one.

One of the issues that can confuse oil buyers is that it is difficult to discern GF-6 from GF-5 based only on the Starburst. The API Donut has more information about what category is met; it defines the API category, the viscosity and the resource conserving attributes of the oil.

On the question of frictional properties of oil, I should have noted that oils do have a coefficient of friction. Its the viscosity, which is a measure of the internal friction between oil molecules and is related to size and general geometry. Bigger molecules and those with lots of large branches and ring structures are more viscous than smaller, slimmer molecules. Theres a lot more to oil than viscosity, but its the starting point for any discussion of oil quality and application.

Budinski replied that he is so interested in this subject that he has organized an ASTM workshop on measuring the friction component of oil, which he is chairing.It will take place in New Orleans at the ASTM Committee D02 meeting to be held December 8-12.

Well, that about does it for this year. Since it is actually early October when Im writing this, dont feel too bad if your excellent question doesnt appear in this column. Ill look to fit it into next years Q&A column or even as a column all by itself. So keep them coming!

Industry consultant Steve Swedberg has over 40 years experience in lubricants, most notably with Pennzoil and Chevron Oronite. He is a longtime member of the American Chemical Society, ASTM International and SAE International, where he was chairman of Technical Committee 1 on automotive engine oils. He can be reached at steveswedberg@cox.net.