Passenger Car Engine Oil Specifications

STM: A Sharper Tool for Engine Tests?


The engine oil industry has various tools to reduce the cost and time required to bring new specifications into the market, including the rules commonly known as base oil interchange and viscosity grade read across guidelines. Over time these rules have evolved to simplify the cost of development and deployment of additive technologies across a wide range of base stocks and viscosity grades.

Their latest iterations are essential to creating ILSAC GF-6, the passenger car engine oil upgrade now expected to see first licensing on May 1, 2020. The industry will spend over $5 million to develop BOI/VGRA guidelines for the new engine tests that define this category.

The basic premise for BOI is that the industry seeks the most severe test conditions, which can allow a formulator to run an engine test and reasonably apply the result to other base stocks. VGRA attempts to find the viscosity grade that presents the most severe conditions to allow an additive technology to read to all other viscosity grades. Not an easy task.

For some tests, base stock has almost no impact, and BOI/VGRA is solely determined by additive technology. An example is the new Sequence IX engine test for lubricants effect on the engine-crippling phenomenon called low-speed pre-ignition. Here, the industry found that additive technology overwhelmed all other parameters, and a single Sequence IX test in an SAE 0W-20 formulation can cover all other base stocks in all ILSAC viscosity grades. For other tests, a mix of attributes can impact the results, including the additive technology and viscosity modifier as well as base stock characteristics like saturates, viscosity and volatility.

Decisions about BOI/VGRA are made using test results from statistically designed matrices, the trial runs that establish each tests precision and reproducibility. Historically, the one test that has to be repeated in all base stocks has been the Sequence III. This oxidation and deposit test has a huge impact on engine oil formulation, and automakers and other stakeholders believe that BOI guidelines for this test may not ensure lubricant formulation across a wide array of base stocks. It was felt that every candidate base stock should have at least one full-length engine test run to define its performance. So in 2003, for example, the matrix to develop VGRA guidelines for the Sequence IIIG required 24 runs at a cost of $35,000 apiece. As LubesnGreases reported at the time, the total tab to the industry approached $1 million.

This led to the development of the Single Technology Matrix, a way to simplify requirements for additive companies needing to approve general market products across a wide variety of base stocks. The question that arose was: How many tests are enough to ensure product performance, given the ever-increasing number of base stocks that are available with very similar performance characteristics?

The original concept for a single technology matrix was brought forward by Lubrizol and was detailed in a 2002 SAE paper by the companys Phil Scinto and Margaret Lemon. Rather than having to examine multiple additive technologies before a BOI guideline can be accepted, an STM allows a single additive package (at a constant treat rate with a single viscosity modifier and in a single viscosity grade) to be deemed acceptable within the range of base oils used in the matrix testing. This is typically seven different base stocks.

Lubrizol had built up a vast database of engine test results and used the Sequence IIIE as an example of how a company can build a matrix of results to generate sufficient data for an additive technology, which then can be used to support many base oils for a given product without further testing.

Why Develop an STM?

Currently, single technology matrices are only approved for the Sequences IIIF and IIIG. It is expected that an STM will be allowed for the new Sequence IIIH, which replaced the Sequence IIIG and will be part of the new ILSAC GF-6A and B specifications and the API SP Resource Conserving category.The IIIH also has been approved for use with older categories where alternative limits have been established.

A single technology matrix is quite important for efficiently qualifying automotive engine oil additive packages in the ever-widening array of base stocks coming onto the market, commented Laura Birnbaumer, automotive engine oil qualification manager at Chevron Oronite. A single technology matrix enhances speed to market overall for all additive packages because the oil formulator does not have to run an engine test in every base oil combination the oil marketer wants to utilize.

A single technology matrix also can help extend the life of an API service category, as once formulators have defined the range of base oil properties of interest for an STM, they are not required to perform additional engine testing for the same technology as long as interchanged base stocks fall within the defined ranges for those properties. Overall, this reduces consumption of the tests precious hardware blocks and spare parts.

Besides helping to trim development costs, having the STM also helps smaller base stock producers to gain formal API approvals in a reasonable amount of time. Even before engine testing, significant effort is spent formulating oils and running the appropriate bench tests to define each formulation. As Mike Reddick, vice president of sales and marketing at Avista Oil Refining and Trading USA, noted, Without the STM program, rerefiners and refiners with small qualified streams could have difficulty attaining approvals for their materials. The program reduces cost for smaller refiners and, more importantly, helps the blender obtain these base stocks at a competitive price.

He added, The STM program is crucial to our long-term sustainability. Without this program, the investment to obtain all the needed approvals for the rerefiner would be substantial and could limit the customers options for these high-quality base stocks.

Birnbaumer observed, Oronite believes that having a single technology matrix procedure for the Sequence IIIH will be key to the broad markets ability to timely establishing qualified finished oils meeting GF-6. All oil marketers, regardless of size, are interested in quickly covering all of their blend facilities to supply qualified product by first licensing.

Besides impacting the initial roll-out of qualified products, single technology matrices also mitigate possible base oil supply crises for oil marketers by facilitating base oil flexibility, so there is less disruption in the market.

Additionally, many large base stock or lubricant marketers may want specific engine test data on their base stock or their lubricant technology. This could influence an additive companys choice of base stocks to be run in the full-length engine test. The STM for the Sequence IIIH will consist of a minimum of seven tests and must be statistically designed to map out a window of coverage for the additive supplier; base stock selection must be carefully managed to ensure the widest coverage and to be statistically significant while meeting both technical and marketing needs.

For example, an additive company may decide to define its matrix using some widely available base stocks, such as API Group II oils from Chevron and ExxonMobil and SKs Yubase Group III. Other stocks may then be chosen because of specific properties, such as saturates, viscosity index, sulfur content or Noack volatility.

Not Everyone Is Convinced

Additive companies and most base stock suppliers appreciate having this procedure in their tool kit, but there are some areas where it may not be allowed. LubesnGreases asked Angela Willis, of Willis Advanced Consulting and formerly of General Motors, how automakers view it. Not too many OEMs really understand what a single technology matrix is and the methodology of how it is approached, she replied.

If an OEM has their own specification for their service- or factory-fill engine oils, and that specification contains requirements over and beyond an industry standard, then they are likely going to require having their own data point and not allow for single technology matrix use.

Perhaps more openness to educating the OEM by the additive companies, and involving the OEM when constructing a single technology matrix program, could build trust and comfort, which could possibly lead into an increase in acceptance regarding the use of single technology matrices with factory-fill or service-fill programs, she suggested.

Although there can be advantages to using an STM, such as having an additive that can meet the performance needs across many base stocks available in the marketplace, Willis feels that it could possibly lead to being overkill, in terms of the additive package, for a given engine oil performance parameter, with trade-off of a different performance parameter.

As an example, in order for a given single technology matrix to always pass the Sequence IIIH, the technology takes a sacrifice in fuel economy, to where it may just barely pass the Sequence VIE fuel economy test. I believe there is some level of trade-off in STMs in order to allow them to perform in a broad range of base oils.

This concern underscores the fact that when adding dispersant or detergent components to improve deposit protection, these same components can be debits when running a fuel economy test. It does not mean technologies cannot achieve fuel economy-it just may be more difficult or may not provide as much fuel economy improvement as a technology optimized around a single or just a few base stocks.

The industry is working to approve an STM for the Sequence IIIH test and improve API 1509 Annex R, which defines the protocol for developing an STM. The API Base Oil Interchange/Viscosity Grade Read Across Task Force of the API Lubricants Group has formed a team to investigate an STM protocol for the Sequence IIIH, Birnbaumer pointed out, including any changes in test-specific base oil properties of interest and other areas of non-clarity in the original Annex R in API 1509 identified by individual team members.

Single technology matrix design is made complex by an increasing number of base oil properties of interest that have a spread requirement as well as areas of apparent contradiction in the current version of Annex R, she continued.

When creating and applying a single technology matrix, an oil formulator must adhere to the tests viscosity grade read across guidelines. Oronite finds the current Annex R is clear about covering both Group II and Group III within an STM. A single technology can have multiple STMs to cover unique viscosity grades (such as SAE 0W-XX), or an additive company can have one STM to cover most viscosity grades and run additional Sequence IIIH tests as needed.

Breaking Through

It appears that changes to Appendix R to cover the STM and include the new IIIH test should be completed in the second half of this year and be ready for use well before product licensing begins for ILSAC GF-6. There were some concerns with regards to VGRA for the Sequence IIIH, which could have created some program deployment complexity.

But as Birnbaumer told LubesnGreases, The concerns around the IIIH have been resolved, and a new Sequence IIIH VGRA proposal that was presented at the April Lubricants Group meeting, which removed the need for viscosity modifier bracketing, was accepted. From Oronites perspective, we hope the path to a Sequence IIIH STM is more straightforward now that this issue has been fixed.

Mike Reddick is hopeful, too: Avista feels the Sequence IIIH test should be expanded to the STM program. The oil thickening and piston evaluation, although more stringent for API SP and GF-6, can be analyzed similar to the current SN+/GF-5 category.

Could General Motors new GMOD oxidation and deposit test-which is mandatory for its proprietary Dexos1 Generation 2 engine oil specification-also get the STM treatment, given all the base stocks that might be used in those products? Angela Willis responded guardedly: If a given additive company involves GM up front in the STM planning in terms of defining the parameters and the window, openly shares the data with GM, and if the STM can meet the rest of the requirements to GMs acceptance criteria, then GM may possibly accept STMs for the GMOD. An STM might also be simpler from a VGRA viewpoint, as GM and other OEMs have little interest in viscosity grades heavier than SAE 5W-30.

Based on all the feedback, it appears the STM will live on for the Sequence IIIH test and continue to help bring lubricants to market in a cost-effective manner. All the major additive companies appear to use STMs to field their general market technologies, and it is clear this tool is valuable-especially for a general market program requiring coverage in many base stocks across the globe.

So far, additional STMs have been limited to the Sequence III test, but if the need arises, there is no reason the concept could not be extended elsewhere. And the potential savings are mouth-watering. An STM for the IIIH, for example, might be defined with the minimum of seven base stocks, versus a full program needing to cover a minimum of 20 base stocks. Thats 13 test runs saved at a cost of approximately $60,000 per test-nearly $800,000 per STM-not to mention all the other bench test work, time and resources saved.

Steve Haffner is president of SGH Consulting LLC. He has over 40 years of experience in the chemical industry, primarily with Exxon Chemicals Paramins and Infineum USA. He specializes in engine oil formulation and marketing. Contact him at or 908-672-8012.