In-Service Low Temperature Pumpability of Crankcase Lubricants- Effect of Viscosity Modifiers

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. It may not always be possible or practical to compensate for the poor performance of this latter class of lubricants with pour point depressants.