Chevrolet Fleetmaster Series 1947 Owner's Manual page 48

" PREMIUM MOTOR OIL, this term shall be used to
designate an oil having proved oxidation stability and
bearing corrosion preventive properties. Oils of this type
are generally suitable for use in internal combustion
engines where operating conditions are such that regular
oils do not give satisfactory service."
"HEAVY-DUTY MOTOR OIL, this term shall designate
an oil having proved oxidation stability, bearing corrosion
preventive properties, and detergent-dispersant character-
istics. Oils of this type are generally suitable for use in both
high speed diesel and gasoline engines under heavy-duty
service conditions."
Regular, Premium and Heavy-
Duty Oils-The
REGULAR or straight mineral motor oils
are satisfactory for use in average passenger-car service under
normal driving conditions. These are considered to be a combina-
tion of low and medium speed driving with only an occasional
long run at high speed.
Under more severe driving conditions where the engine is
required to develop more nearly full power for a much larger
percentage of the time, as for example in mountain climbing
and in sustained high speed driving, the PREMIUM MOTOR
OILS are recommended.
The HEAVY-DUTY OILS, which are recommended for use
in heavy-duty truck and bus diesel and gasoline engines, are
equally satisfactory for use in passenger-car engines under the '
same operating conditions for which the PREMIUM MOTOR
OILS are recommended .
. ' When to Change Crankcase Oil-
Oils have been greatly improved, driving conditions have changed,
and improvements in engines, such as the crankcase ventilating
system, have greatly lengthened the life of good lubricating oils.
However, to insure continuation of best performance, low main-
tenance cost and long engine life, it is necessary to change the
crankcase oil whenever it becomes contaminated with harmful
foreign materials. Under normal driving conditions draining the
crankcase and replacing with fresh oil every 2000 to 3000 miles
is recommended.
Under the driving conditions described in the following para-
graphs, it may become necessary to drain the crankcase oil more
frequently. '
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