The Role of the Engine Oil in Cold Weather Starting

An examination of the background history and literature in the field of cold engine cranking is presented. As a result of this review, it is concluded that a maximum critical engine oil viscosity exists which, when exceeded, will prevent engine starting. The present SAE Viscosity Classification System, which covers W grades based on ASTM viscosity-temperature extrapolation, is applicable to straight mineral oils with respect to ease of engine starting but can be in error (too high or too low) for multigraded oils containing polymeric VI additives. Any laboratory instrument proposed to serve as a new basis for the SAE W grades must be judged on its ability to predict engine performance. To date, it appears that the L-49-663 engine cranking research technique developed by the Coordinating Research Council (CRC) represents the best approach for generating data on oils in engines which can be used to judge the ability of laboratory instruments to classify oils with regard to startability.