For correct engine lubrication a high grade, well refined oil is absolutely essential.
As a guide to the proper viscosity or body of oil for summer and winter conditions, which vary for different territories, the lubrication charts of reputable oil companies should be consulted. In general, an oil having the body of S. A. E. viscosity No. 40 corresponds approximately to our M-515-A and B and is accordingly recommended for summer use.
For winter use, S. A. E. oil specifications No. 20 can be used. It is necessary, however, for winter use, that such an oil have a low cold set.
A large number of oil companies are stamping containers and indicate on their charts S. A. E. numbers. This practice is desirable because of the fact that it assists the owner to obtain the proper oil for his engine.