The development of the Scanning Brookfield Technique (SBT) has generated new understandings of the rheology of automotive lubricants at low temperatures, particularly in engine oils and even more particularly in regard to the phenomenon of air-binding, which is believed caused by oil gelation. The latter phenomenon has been directly implicated in the pumpability failure of engines in the field and in cold-room simulation. This paper first traces the prior studies and use of the Brookfield Viscometer at low temperatures -- work which generated low-temperature information on lubricants and methods ultimately leading to the development of the Scanning Brookfield Technique (SBT) and the application of this technique to the detection of the presence and severity of gelation at lower temperatures of automotive operation. The SBT has shown close correlation with the Pumpability Reference Oils (PROs) used in the ASTM engine pumpability study and detected significant gelation in all known field- or engine-failing oils. The most recent studies generated by the SBT show that the technique permits the measure of new criteria of gelation, two of which are 1. Gelation Index, a measure of maximum gelation severity closely correlated with the yield stress of a lubricant, and 2. Gelation Temperature, the temperature at which the Gelation Index is generated.

This paper summarizes the published information on the relationship between oil viscosity and engine performance that may be of use in developing a new engine oil viscosity classification system. The specific engine performance factors and associated variables considered are wear, oil consumption, fuel economy, hot starting, cold starting, low temperature pumpability, noise, and shear stability.

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The most widely used and effective anti-wear/anti-oxidation additives in engine oil contain phosphorus that can partially volatilize during engine operation. Unfortunately, volatile phosphorus in the exhaust stream degrades the function of the exhaust catalyst in reducing air pollution. Earlier studies in a special volatility bench test using the Phosphorus Emission Index have shown that phosphorus volatility is not related to engine oil volatility or to phosphorus content in the unused engine oil. At the time, it had been speculated that this unexpected lack of correlation with initial phosphorus concentration could be explained by 1) the effects of other engine oil additives and/or 2) variations in the phosphorus additive chemistry. The first speculation was relatively recently confirmed by taxi fleet studies of catalyst degradation by phosphorus-containing oils by the Ford Motor Company. It remained to determine if differences in phosphorus additive chemistry were also a factor, and this is the subject of the present study.

A series of engine oil samples collected during a study of their Phosphorus Emission Index values were analyzed by 31 P Nuclear Magnetic Resonance Spectroscopy. (The PEI analyses themselves were presented in an associated paper [1]). NMR spectra were generated to obtain and explain the mode of formation and identity of the phosphorus-containing species in the volatiles generated during the Selby-Noack volatility test and compare these species to those found in both the fresh oil and the residual oil remaining after the volatility test.