THE factors involved in cold starting of automobile engines, including the effects of temperature and oil viscosity on cranking speed and torque, have been known for many years. Many papers have been presented before the various Sections of the Society on these subjects.
The S.A.E. crankcase-oil viscosity-numbers, which were adopted in July, 1926, provided for the classification of the lower-viscosity oils at 130 deg. fahr. and the higher-viscosity oils at 210 deg. fahr. It was recognized by 1930 that a classification for winter oils must be based on the viscosity of the oil at the starting temperature, and work was started on this problem. In June, 1933, the 10-W and 20-W oils, which are classified in accord with their viscosity at 0 deg. fahr., were adopted for publication and trial.
The results of the use of these oils during the winter of 1933-1934, together with their advantages, are discussed. The data show that these oils are necessary for cold starting, provide adequate lubrication and improved performance and give reasonable oil mileage.
Although higher-viscosity oils give more miles per gallon of oil, by far the most important factor in oil consumption is engine speed. The lower-viscosity oils, that are required for winter operation, reduce engine friction; and the total cost of oil plus gasoline, using oils of lower viscosity, may be less than when using oils of higher viscosity.