Search Results

The Viscosity Index (VI, ASTM D2270) has a long and widespread history as a rating scale for the viscosity-temperature behavior of lubricants. However, the method has serious technical deficiencies which can lead to misleading conclusions. We have examined alternatives to the VI scale in an effort to more accurately characterize the viscometric behavior of modern lubricants, which are formulated with highly refined base oils and advanced polymers. We have found that the VI method can actually mask improved viscosity-temperature behavior for certain highly additized polymer-containing lubricants. We examine two different methods, the Roelands Slope Index and the Proportional VI, as an alternative to VI. It is important for lubricant developers and consumers to be aware of the limitations of the VI scale in describing the viscometric qualities of modern, high performance lubricants.

The continuing push for improved fuel economy, reduced carbon emissions, and lower operating costs has resulted in higher operating temperatures for axle lubricants in passenger cars and commercial vehicles. These higher operating temperatures, in turn, have placed more severe demands on the thermal & oxidative performance of axle lubricants. A number of industry-standard, laboratory methods exist to evaluate this key performance parameter. This paper discusses the use of laboratory methods to evaluate oil service life. We examine the behavior of five commercially available axle lubricants in the CEC L-48 oxidation test (Apparatus A). The oils were chosen so that different additives and base oils could be compared. We evaluated both the effect of time and temperature on the oxidation behavior. In agreement with previous studies, we found that infrared (IR) spectroscopy provides a convenient and meaningful way to track the extent of oxidative degradation.

The Viscosity Index (VI), now defined by ASTM D 2270, is a relative number intended to represent the degree of change in viscosity versus temperature for lubricating oils. The basis for the rating scale, which was first defined in 1929, is a comparison of a candidate oil with two reference oils, one defined as “100 VI” and the other defined as “0 VI”. The VI scale has been widely used since its inception because of its simplicity and good correlation to a number of physical and chemical properties. However, the rating method suffers from a number of fundamental problems which are not realized by most users of the method today. This paper examines the assumption basis and historical development of the VI scale with an emphasis on the arbitrary and non-systematic manner in which the “100 VI” and “0 VI” reference series have been defined and modified over the years.

We have compared five different, commercially produced, API Group III base oils in a next-generation, OEM automatic transmission fluid (ATF) formulation. One objective of this work is to understand the impact of base oil selection on the performance properties of finished ATF. This may help us to develop technically sound criteria for allowing interchange among premium Group III base oils in both factory-fill and service-fill ATFs. The performance data, measured from lab bench tests, include such properties as seal swell, low temperature viscometrics, oxidation life, and LVFA static and dynamic friction. Certain properties of the base oils, such as low temperature viscosity and oxidation stability, have a strong impact on the ATF performance. However, there are many chemical similarities between the Group III base oils, and this results in little to no differences observed in many performance areas.

Over the past several years, economic pressures have driven fleets to substantially increase their maintenance intervals. To meet this challenge, both the Original Equipment Manufacturers (OEMs) and the lubricant suppliers have developed new and better products to give fleet users the benefits of extended service intervals, while at the same time maintaining equipment life and providing the potential for reduced operating costs. Through the selection of proper lubricants, fleets can now minimize their total operating costs with products that meet the OEM extended service specifications, have demonstrated equipment durability, and are formulated using base oil and additive components to minimize the cost of the lubricant. This paper will examine the options available for formulating extended drain transmission and axle lubricants. It will explore the selection of the lubricant base oil as well as the additive system.