Assessment of Ageing Mechanisms in Lubricants and Their Effects on Retained Low Temperature Pumpability of Top Tier Oils

Low temperature pumpability is an important requirement for engine lubricants. It ensures that sufficient oil reaches the parts of the engine requiring wear protection on engine start-up. Until recently, most industry emphasis has been on the low temperature pumpability of the fresh oil. However, the oil can undergo a number of changes during its lifetime in the engine which adversely affect low temperature pumpability. Industry stakeholders are now expressing concerns about the potential risk of engine failures due to deterioration of low temperature pumpability of oils during their life cycle in the engine. Concerns have also been raised over the last few years that the move to Group III base stocks, while improving many of the properties of oil formulations, may also impact their retained low temperature pumpability. The increasing use of biodiesel, particularly when coupled with extended oil drain intervals, has also been shown to impact low temperature pumpability performance of some oils.

This paper addresses the effect of emerging trends in lubricants and fuels as well as of the lubricant service cycle and extended drain intervals on retained low temperature pumpability. We first determine the level of ageing of the lubricant in typical field applications as well as in service cycles that tend to lead to low temperature pumpability failure. We show that the loss of low temperature pumpability in the field can be due to a number of different mechanisms, and we explore the contribution of each of these ageing routes to the low temperature pumpability of the lubricant. We show that by carefully matching ageing parameters to those seen in the field we can not only replicate field ageing conditions but also low temperature pumpability behavior.