New Mini-Rotary Viscometer Temperature Profiles That Predict Engine Oil Pumpability 850443

The Mini-Rotary Viscometer (MRV) procedure, ASTM D3829, was designed to predict the pumpability characteristics of engine oils. The viscosity and yield stress measurements determined by this instrument correlate with the 16 hour cold-soak laboratory engine test results that were carried out in a joint ASTM/SAE program in the early 1970’s. However, several oils that had passed the ASTM D3829 procedure and the viscosity classification requirements in SAE J300 SEP80 caused pumpability field failures in engines during the winters of 1980 through 1983. These oils can be divided into two types of failures: those which failed after an overnight exposure to low temperature, and those that require several days exposure before problems developed. This paper describes the development of a series of temperature profiles for use with the MRV that clearly predicts the low temperature characteristics of these two groups of oils. The sensitivity of these oils to different cooling conditions is explored. Cooling profiles have been developed that identify ail of the known field failing oils to date.