A Low-temperature Study of the Relationship between Engine Cranking Speed and Lubricant Viscosity

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Abstract
The viscosity of motor oils at low temperatures strongly affects the cranking speed of the motor. In a previous paper the author has shown that the viscosity characteristics of motor oils at low temperatures may be unusual, especially when they contain Viscosity Index Improvers. In this paper the author has analyzed the results of 250 cranking tests on two different V-8 engines conducted at temperatures from +3 to −35 F, using three fluids, two of which contained Viscosity Index Improvers. The data seem to indicate an exponential relationship between the cranking torque M, and the cranking speed, N, and viscosity, μ, such that M = c(μNb) in which b and c are constants and b ≃ 0.5. Further results of this study strongly indicate that the correlation is significantly better between cranking speed and viscosities measured at shear rates of approximately 2000 sec −1 than the correlation between these cranking speeds and viscosities determined by the ASTM extrapolation technique (Walther equation), or by a recent empirical modification of this technique.

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