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Mechanical degradation of polymeric additives in lubricants has been a topic of extensive study since complex formulations were introduced to reduce the temperature dependence of viscosity. Many devices, which are able to shear polymers, have been tested for their abilities to simulate the degradation observed in engines and other lubricated systems. Conclusions drawn from these studies are often ambiguous as they depend on the test protocol and method of data analysis. In this work, a simple expression based on probabilistic arguments is used to describe kinematic viscosity data from a variety of degradation simulators. This expression provides a method of comparing extent and rate of degradation for different simulators.

The use of specially formulated engine oil is now an acceptable means of increasing the fuel efficiency of a vehicle. In principle, many of the same arguments used to justify their performance can also be applied to gear lubricants. Viscometrics and shear stability are discussed as they pertain to proper polymer selection for gear lubricant service. The fuel efficiency effects for three experimental lubricants relative to a commercial SAE 90 grade fluid were determined from a 3.1 million mile (5.0 million km) fleet test involving heavy duty trucks in normal service. The statistical techniques used to design this fleet test and analyze the data are presented, and the physical interpretation of the results is discussed. The results show that use of properly selected multi-grade gear lubricants can result in significant reduction in fuel consumption.

Temporary shear loss characteristics of multigraded engine oils were measured in a newly developed engine oil pump rig. Correlations of the results with high pressure capillary viscometry data indicate that the test apparatus generates shear rates in the range of 2-3 × 105 s-1. One advantage of this technique over similar mechanical approaches is that the test rig causes virtually no permanent shear degradation. Test results are reported for a variety of polymer types, and the relationship of permanent and temporary shear losses is discussed.

A continuous, high speed road test has been found to accurately assess the shear stability of motor oils under all types of engine operation. It has also been demonstrated that a methacrylate polymer of sufficiently low molecular weight is completely shear stable under shearing conditions of the high speed road test. A road shear stability survey of commercial multi-graded oils has shown that some oils fail to produce the expected viscosity decrease due to oil oxidation. Preliminary road tests in diesel engines have shown the shear stability losses in polymer-thickened oils similar to those produced in the gasoline engines. Shear stability studies in automatic transmission fluids by both bench and field tests have shown that this application is substantially more severe than the engine in shearing polymeric V.I. improvers.

The role of non-Newtonian fluid characteristics in lubricant performance was studied in a variety of V.I. improved lubricants. It was shown that proper choice of V.I. improver can yield a lubricant which undergoes both small temporary and permanent viscosity losses, thus giving nearly Newtonian behavior but with high and low temperature performance advantages over straight mineral oils. In hydraulic fluids, it was shown that different V.I. improvers resulted in varying amounts of internal leakage in both vane and internal gear pumps. In the case of vane pumps, the favorable Newtonian characteristics of shear-stable V.I. improvers assured outstanding pumping performance. It is believed that control of transmission leak-down was primarily responsible for the favorable influence a shear-stable V.I. improver had on the maximum transmission sump temperature at which the wide-open throttle 2-3 upshift will take place.

A multi-vehicle chassis dynamometer procedure for evaluating an engine oil for fuel economy effects has been accepted by ASTM and the lubrication industry with reservation. The reservation stems from the high test cost, the poor repeatability/reproducibility, and a concern that some additive chemistries are not being fairly evaluated. Recognizing these concerns, ASTM Committee D-2 has agreed to continue development work, but the thrust will now be toward a Sequence type, dynamometer engine test. The work which will be described here is part of a statistically designed study intended to screen operating conditions and hardware for their effects on fuel efficiency and test reliability. Three ASTM FEEO oils were evaluated relative to the FEEO reference oil HR-2 in a 2.8 L V-6 engine. Correlation with results from the 5-car test development program will be presented, as well as the results of the analysis for operating condition effects and sources of test variability.