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A range of tools including analytical, bench, and engine tests have been used to investigate the viscosity increase mechanism and formulation appetite of the Sequence IIIG engine test. As commonly observed with high temperature tests, the Sequence IIIG has a strong appetite for antioxidants. Base oil also has a strong impact. Base oil volatility has a direct physical impact on viscosity due to the evaporation of light base oil components and the resultant increase of non-volatile additive components. Volatility characteristics are dependent on the distribution of volatile fractions. The relative oxidation and volatility contributions to viscosity increase have been compared between the Sequence IIIG and Sequence IIIF. The impact of base oil volatility is greater in the Sequence IIIG than the Sequence IIIF test.

Modern Passenger Car Motor Oils (PCMOs) are formulated to provide superior wear, oxidation, and deposit control under the most demanding driving conditions. In most PCMOs, zinc dialkyldithiophosphate (ZnDTP) has been the dominant antiwear and antioxidant agent for well over 50 years. Unfortunately, the phosphorus in ZnDTP may partially deactivate the exhaust emission catalyst. To ensure that the catalysts function for at least 120,000 miles, engine manufacturers are exploring phosphorus limitations for upcoming PCMO performance categories. This paper explores the antiwear film formation of low phosphorus engine oils using the Electrical Contact Resistance bench test. A prototype ILSAC GF-4 formulation blended with varying amounts and types of ZnDTP was tested at temperatures typical of operating engines. Secondary ZnDTP was found to produce the best films under the broadest temperature range.

Of all the performance tests in the current International Lubricant Standardization and Approval Committee (ILSAC) GF-3 and GF-4 categories, the Sequence IIIF and Sequence IIIG are among the most difficult for the formulator. The Sequence III engine dynamometer tests place a premium on oxidation, high-temperature deposits, and valve train wear control. Besides appearing in the North American Passenger Car Motor Oil (PCMO) specifications, the Sequence III is required for European gasoline engine oils, for American Petroleum Institute (API) diesel engine oil categories, and for base oil interchanges (BOI) among licensed engine oils. The ability to screen antioxidants for the Sequence III is of special interest for developers of engine oil technology. Antioxidants are the single most expensive component and the search for cost-effective oxidation control is among the top technical hurdles for the North American PCMO categories.

With the impending development of GF-6, the newest generation of engine oil, a new standardized oil oxidation and piston deposit test was developed using Chrysler 3.6 L Pentastar engine. The performance requirements and approval for passenger car light duty gasoline engine oil categories are set by the International Lubricants Standardization and Approval committee (ILSAC) and the American Petroleum Institute (API) using standardized testing protocols developed under the guidance of ASTM, the American Society for Testing and Materials. This paper describes the development of a new ASTM Chrysler oxidation and deposit test that will be used to evaluate lubricants performance for oil thickening and viscosity increase, and piston deposits.