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This paper describes the results of a series of tests on a heavy-duty truck diesel engine using conventional and low viscosity lubricants. The objectives were to explore the impact of reducing lubricant viscosity on wear, friction and fuel consumption. The radiotracing Thin Layer Activation method was used to make on-line measurements of wear at the cylinder liner, top piston ring, connecting rod small end bush and intake cam lobe. The engine was operated under a wide range of conditions (load, speed and temperature) and with lubricants of several different viscosity grades. Results indicate the relationship between lubricant viscosity and wear at four critical locations. Wear at other locations was assessed by analysis of wear metals and post test inspection. The fuel consumption was then measured on the same engine with the same lubricants. Results indicate the relationship between oil viscosity and fuel consumption under a wide range of operating conditions.

This paper investigates the phenomena of gel formation and poor filtration performance of engine oils containing certain olefin copolymer (OCP) viscosity modifiers (VMs). Low temperature pilot plant and bench scale filtration tests have been used to study the filtration behaviors of a wide range of low-ethylene and high-ethylene OCP VMs at various temperatures but with particular focus on the performance at 0°C. Further, rheological studies have been carried out on fully formulated oils as well as on PAO solutions of these polymers to understand the effect of thermal history on the polymer solution behavior over a broad range of temperatures. These studies suggest that many high-ethylene OCPs are prone to the formation of polymer aggregates in oil solutions. Long crystalline polyethylene segments present in high-ethylene OCP molecules are believed to interact with similar segments in neighboring molecules, leading to the formation of aggregates.

Low temperature pumpability has been an important requirement of engine oils for the past two decades. However, until recently this requirement has applied only to fresh oils. Pumpability can deteriorate significantly during oil's life cycle in the engine. Many factors such as combustion byproducts and oxidation can influence oil pumpability at low temperatures. This paper examines the effects of in-service aging on low temperature pumpability of oils using a variety of industry and proprietary engine tests. In particular, the paper investigates the role of viscosity modifiers in the retention of satisfactory low temperature performance in service. The data show that oils formulated with certain types of viscosity modifiers tend to maintain robust low temperature pumpability throughout their entire stay in the crankcase. Lubricants formulated with another class of viscosity modifiers tend to lose their low temperature performance quite early in their life cycle in the engine.