The contribution to measured viscosity at 0 F of a variety of additives used in modern engine oils has been studied using a cone-plate viscometer which correlates well with engine cranking measurements. The major contributors were found to be the base oils, the ashless dispersant, and the viscosity index (VI) improvers. In the latter case, the contribution was shown to be related to the efficiency of the VI improver with VI improvers of low efficiency contributing substantially more than those of high efficiency. Summing the contributions of the additives in a given base led to close prediction of the viscosity at 0 F.
