Assessment of Low Temperature Viscosity Performance in Modern Engine Oils 2013-01-2565
Control of oil viscosity increase at low temperature, which derives from the wax crystallization behaviors of various formulation components, is a critical performance criterion in modern engine oil lubricants. Failure to manage viscosity increase will result in high oil viscosity and poor oil pumpability under cold start conditions, and eventually may lead to catastrophic damage to the engine. The importance of oil low temperature rheology gained further attention when the ILSAC GF-4 specification implemented an aged oil low temperature viscosity limit to guarantee performance retention during operation. This requirement continues in ILSAC GF-5 and is regarded as one of the key benchmarks of modern passenger car engine oils.
Pour point depressants (PPDs) are polymeric additives that help alleviate viscosity increase under tcold climate conditions through interaction and control of wax crystallization growth. With increasingly diverse base stock supplies and quality standards, different wax characteristics of formulation components, and various testing methods (fresh and aged oils), achieving robust and consistent low temperature performance can be a challenging task for engine oil formulators. Consequently, appropriate PPD selection is imperative to guarantee this consistency.
In this paper, conclusions drawn from the evaluation of a comprehensive set of engine oils will first be presented and discussed to illustrate the importance of low temperature performance. We will then consider the use of polyalkylmethacrylate (PAMA) PPDs in engine oil formulations and discuss selection guidelines to meet the stringent modern engine oil cold flow standard including the Romaszewski Bench Oxidation (ROBO) test. ROBO, which was developed by Evonik Oil Additives to simulate Sequence IIIGA engine tests, is currently listed in the ILSAC GF-5 specification as one of two methods to generate aged oil for low temperature property evaluation. This paper will report results using the ROBO test to assess the effect of aging processes on engine oil low temperature properties (MRV TP-1 viscosity). The influence of oil aging on PPD appetite will also be discussed.