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This paper outlines the second part in a series on the effect of polymeric additives commonly known as viscosity modifiers (VM) or viscosity index improvers (VII) on gear oil efficiency and durability. The main role of the VM is to improve cold temperature lubrication and reduce the rate of viscosity reduction as the gear oil warms to operating temperature. However, in addition to improved operating efficiency across a broad temperature range compared to monograde fluids the VM can impart a number of other significant rheological improvements to the fluid [1]. This paper expands on the first paper in the series [2], covering further aspects in fluid efficiency, the effect of VM chemistry on these and their relationship to differences in hypoid and spur gear rig efficiency testing. Numerous VM chemistry types are available and the VM chemistry and shear stability is key to fluid efficiency and durability.

Specific frictional properties are essential to provide correct and pleasurable shifting in a manual transmission. Synchroniser rings are being manufactured from an increasingly wider range of materials, and it is important to understand synchroniser-additive interactions in order to develop tailored lubricants that provide the desired frictional performance. This paper describes a study of the interaction of various friction modifier additives with a range of synchroniser materials in order to better understand the potential to develop lubricants that provide optimal frictional performance across a wide range of manual transmission-synchroniser systems.

Panel cokers have been used for a number of years for the evaluation of lubricant formulations with respect to thermal oxidative stability. There are, however, a number of drawbacks to the technique, particularly related to variability of the test and correlations to real engine performance. As a consequence of this, work has been undertaken to develop a new thermal oxidative screen test which provides greater flexibility and better correlation to engine tests. The glass panel coker test has been developed from a combination of several screen tests, and consists of a heated sump, where the lubricant is aerated and has NO2 additions, and from which oil is circulated over a high temperature metal surface. The apparatus largely consists of standard laboratory glassware, and as such is easily customisable to incorporate additional features, for example simulated fuel or water dilution.