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October 4, 2017

Volume 17 Issue 52

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Industry Strives to Correlate Engine Tests

When the auto and oil industries develop new engine tests for automobile engine oil specifications – as is happening now – there is always work that needs to be done to correlate replacement tests to the tests that they replace. The recent decision to develop API SN-RC PLUS as an interim upgrade there is sudden pressure on an ASTM committee to develop correlations between several new and existing engine sequence test procedures. The Category Life Optimization Group reported Sept. 14 that work on some tests is progressing well while others could drag on for months.

Correlation is necessary when the industry replaces engine tests. While the new tests may be developed primarily for new specifications, they are also become part of the requirements for existing specifications, especially when tests for existing specs get retired because of hardware running out. In such cases, oils known to have achieved certain results on older tests are used in replacement tests to see how the scores on the older test correlate to the newer one.

CLOG Chairman Thom Smith, of Valvoline, gave a progress report on correlation work at the Sept. 14 meeting of API’s Lubricant Group. CLOG is part of ASTM’s Passenger Car Engine Oil Classification Panel. Smith said work is progressing nicely on the correlation of three tests for high-temperature protection against oil thickening and varnish deposits along with antiwear protection – the Sequence IIIF, Sequence IIIG and the Sequence IIIH. The Sequence IIIF is run as a part of API categories SJ, SL, CH-4, CI-4 and CJ-4.  The correlation between Sequence IIIF and Sequence IIIH is on track to be completed and available by December, while the correlation from the Sequence IIIG to Sequence IIIH has already been completed and reported.

CLOG has determined that wear results in the Sequence IIIF, Sequence IIIG and Sequence VE could be waived for oils that have a phosphorus content of at least 0.06 percent and that have passed the Sequence IVA or IVB tests. The Sequence IVB test to simulate stop-and-go driving is under development to replace the Sequence IVA. The provision for a minimum phosphorus level would apply to API engine oil categories from API SJ to SN and also include GF-5.

CLOG is concerned that Sequence IVA and Sequence IVB may be so different that a correlation may not be able to be established. Intertek’s Bill Buscher, chairman of the Sequence IV Surveillance panel, told the Lubricants Group there is sufficient Sequence IVA test hardware available to cover the industry until the introduction of GF-6, the next passenger car engine oil specification from the International Lubricant Standardization and Approval Committee, which is now delayed until late 2019. A test development committee is conducting matrix testing meant to demonstrate that the IVB can differentiate between different oils of different performance levels, but that work is not expected to be completed and analyzed until the first quarter of 2018.

The Sequence VH is being readied to take over from the Sequence VG to measure low-temperature sludge, wear and varnish control, and sequences VIE and VIF will soon be ready to replace the VID test for fuel economy.

Smith said correlations between the Sequence VH and Sequence VG were in the hands of statisticians, and that they expected to recommend sludge and varnish ratings by the end of September. These correlations will apply to categories API SJ through API SN and also include GF-5.

The Sequence VID is the test requiring correlation most critically since it has been unavailable since May 10 of this year. It was a part of the API SN and SN-Resource Conserving categories as well as GF-5. There are several aspects that need to be addressed of a correlation from the Sequence VID to the Sequence VIE and Sequence VIF. For oils with high temperature high shear rate viscosities of at least 2.6 centiPoise, CLOG is awaiting completion of a Sequence VIE survey of commercial SAE 0W-20, SAE 5W-20, SAE 5W-30 and SAE 10W-30 oils, conducted as a means of gaining correlation between the two tests. Phase 1 of this correlation matrix has been completed. Phase 2 has just completed an eight-test survey, and the results of this phase are being analyzed. 

Because of the recent addition of SAE 0W-16 viscosity grades, Sequence VIF is going to be included in further work to determine appropriate limits for SN, SN-RC and SN-RC Plus. SAE 0W-16 has high-temperature high-shear viscosity of less than 2.6 cP and is not currently covered by Sequence VID.

All of this work has taken on new meaning with the approach of API SN Plus and SN-RC Plus. At this point it is not known whether the addition of the low speed pre-ignition (Sequence IX) test will require reformulation of current GF-5 and API SN-RC products. There is some research that indicates a possible reformulation will be needed, in which case it will be necessary to run all tests to gain new approvals for SN Plus and SN-RC Plus. There may be a major reformulation needed to bring all oil marketers up to speed on this new category.