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Today's engine oil formulators must continually balance performance in various low temperature rheological tests including Mini Rotary Viscosity (MRV), Scanning Brookfield Gel Index, Pour Point, etc. Frequently, optimization against one low temperature specification leads to sub-optimal performance in another, a direct consequence of significant differences in the cooling rates and shear rate/shear stress regimes employed in the tests. To better understand the implications of these differences in rheological properties, laboratory and vehicle low temperature tests were undertaken on a series of SAE 5W-30 oils with different combinations of gel index and MRV properties, but no direct correlation between the two. Full scale motored pumpability testing in pairs of modern 4- and 8- cylinder engines were conducted at ambient temperatures between -35 and -38°C (below the anticipated minimum start temperatures (MST's) of the vehicles).

The estimation of fuel economy benefits gained through improved engine oils using ASTM test procedures is expensive and time consuming. This paper describes a methodology to predict ASTM Sequence VI and VIA fuel economy based on laboratory bench tests. High shear rate viscosities were measured using a tapered bearing simulator and boundary friction coefficients were measured using a Plint reciprocating machine at temperatures used in Sequence VI and VIA tests. Weighted viscosities and weighted friction coefficients were calculated from these measurements using weighting factors identical to those used in the Sequence tests. The measured Sequence VI and VIA fuel economy numbers were correlated with the weighted viscosities and weighted friction coefficients. An excellent correlation was observed between Sequence VIA fuel economy and weighted high shear rate viscosities and friction coefficients whereas a reasonable correlation was observed for Sequence VI fuel economy.