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The SAE Engine Oil Viscosity Classification (EOVC) Task Force has been gathering data in consideration of extending SAE J300 to include engine oils with high temperature, high shear rate (HTHS) viscosity below the current minimum of 2.6 mPa⋅s for the SAE 20 grade. The driving force for doing so is fuel economy, although it is widely recognized that hardware durability can suffer if HTHS viscosity is too low. Several Japanese OEMs have expressed interest in revising SAE J300 to allow official designation of an engine oil viscosity category with HTHS viscosity below 2.6 mPa⋅s to enable the development of ultra-low-friction engines in the future. This paper summarizes the work of the SAE EOVC Low Viscosity Grade Working Group comprising members from OEMs, oil companies, additive companies and instrument manufacturers to explore adoption of one or more new viscosity grades.

Global environmental and economic concerns of today's world dictate strict requirements for modern heavy duty engines, especially in emissions, noise control, power generation, and extended oil drain intervals. These requirements lead to increased stresses imposed on lubricants in modern heavy duty engines. At the same time, the original equipment manufacturers (OEMs) desire additional fuel economy from the lubricating oil, requiring the use of lower viscosity lubricants to minimize frictional losses in the engine. These lower viscosity oils are subjected to increased stresses in the engine and need to provide robust performance throughout their lifetime in order to protect engine parts from wear and damage. One of the most important lubricant qualities is to maintain viscosity throughout the drain interval and thus provide continuous engine protection.

An unprecedented global focus on the environment and greenhouse gases has driven recent government regulations on automotive emissions across the globe. To achieve this improvement, Original Equipment Manufacturers (OEMs) have advocated a progressive move towards the use of low viscosity grade oils. However, the use of lower viscosity grades should not compromise engine durability or wear protection. Viscosity modifiers (VM) - polymeric additive components used to tailor the lubricant’s viscometric properties - have been viewed as a key enabler for achieving the desirable balance between fuel economy and engine durability performance. Self-assembling diblock copolymers represent a unique class of VMs, which deliver superior shear stability due to their tunable association/dissociation in the lubricating oil. Superior shear stability ensures that the oil viscosity and its ability to offer reliable engine protection from wear is retained over the life of the oil in the engine.

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.