The effect of lubricants on the starting ability of automobile engines

Abstract

The paper, which is a combination of new and published work, describes tests done in an automotive engine, first to establish the sources of cold cranking resistance, then, by direct measurements of piston assembly friction, to assess the magnitude of the shear stresses imposed there on the lubricant. Comparison is then made with the shearing conditions in two laboratory viscometers used to predict cold cranking characteristics of lubricants. This comparison, made with respect to non-Newtonian oils, leads to the expectation of good correlation between viscometer data and engine cranking data. It is then shown that these expectations are borne out both for large capacity V-8 engines and for smaller European engines and that the latter correlation can extend to starting ability as well as to ease of cranking. The paper stresses the importance of non-viscous sources of cranking resistance and demonstrates that, in terms of starting ability, there are wide, oil-independent differences between engines.