The Scanning Brookfield Technique of Low-Temperature, Low-Shear Rheology -- Its Inception, Development, and Applications

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.