Engine Lubrication - Pontiac 1955 Owner's Manual

Engine lubrication
The terms Regular, Premium and Heavy Duty have generally been
used to designate the types of engine oils supplied by the oil industry
to meet the requirements of various service conditions. These terms
have been replaced by the designations "For Service ML", "For
Service MM", and "For Service MS or DG".
Petroleum based engine oils of type "MS or DG" as supplied by repu
table marketers are recommended for use in our new Pontiac engines.
S.A.E. OIL NUMBER SYSTEM—The numerical designations such
as 10W, 20W and 20, etc., adopted by the Society of Automotive
Engineers, classify lubricating oil only according to Fluidity (viscosity).
The oils with the lower numbers are lighter and flow more readily
than do the oils with the higher numbers. The letter "W" after the
number indicates an oil adapted for cold weather starting. Multi-
viscosity type crankcase oils such as 5W-10W, 5W-20, 10W-20W and
10W-30 are designed to combine the easy starting characteristics of
the lower number with the warm weather operating characteristics of
the higher number.
SELECTING OIL OF THE PROPER NUMBER-An oil should
be used which provides safe lubrication, satisfactory oil economy
under warm climatic conditions, and easy starting at the lowest
36