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. Multi-grade engine oils contain polymeric viscosity modifiers that can be mechanically sheared in the high shear environment of the engine with a resulting drop in viscosity. We evaluate the viscosity behavior of the oils formulated with various viscosity modifiers and the corresponding engine wear in modern Heavy Duty Diesel (HDD) engines in a field trial. The correlation between mechanical shear in the engine and that in the bench test is confirmed. The effect of shear on kinematic viscosity at 100 °C (KV100) and high temperature high shear viscosity at 150 °C (HTHSV150) of both high and low viscosity oils is analyzed.