C. B. Richey, Agricultural Engineering Department
Two important changes have recently been introduced with regard to crankcase oils for both gasoline and diesel engines. One is the development of a new "super" grade oil for automobiles; the other is the revision of the API oil service classifications.
NEW "SE" GRADE OIL
Today's automobile engines run hotter than ever before — and not just because of horsepower. Emission controls, pressurized cooling systems, air conditioning, automatic transmission fluid cooling, sustained high-speed driving, bigger engines with lower compression ratios, trailer towing — all contribute to higher operating temperatures. Prolonged high-temperature operation has caused many of the multi-viscosity oils to thicken excessively between the modern long oil-change periods.
A new top-grade motor oil, designated SE, is now available which retains the cold weather-short distance advantage of multi-viscosity oils but thickens less between changes. SE oil is recommended for most 1972-model cars but can also be used in place of lower grades in older-model cars.
REVISED oi l service classi fications
Motor oils are classified according to engine type and intended use. A standardized letter designation is given for each class to indicate the type of service for which the manufacturer recommends his oil.
The American Petroleum Institute (API) recently revised these oil service classifications, adding the new SE grade and changing the letter designations of the existing grades. The table on
the back shows these changes for both gasoline and diesel engine oils.
Two things should be kept in mind when referring to the API oil service classifications in the table. First, the letter designation alone on a brand of oil only indicates the type of service for which the oil supplier recommends his product and does not necessarily guarantee that it meets the manufacturer's recommended specification or performance test for a particular engine. Thus, the user must still rely on the integrity of the oil supplier.
Secondly, the API classifications are not to be confused with SAE (Society of Automotive Engineers) viscosity numbers. SAE ratings refer to the fluidity of an oil at OOF. in the case of numbers ending with a "W", and at 210©F. in the case of numbers without a "W". Multi-grade oils use special additives which reduce the change in viscosity with temperature. Therefore, a multigrade oil may rate as SAE 10W for cold-weather starting at 0°F. but still maintain body for an SAE 30 rating at 210°F.
A SPECIAL WORD TO TRACTOR OPERATORS
Multi-viscosity oils may be beneficial for light-duty usage of farm tractors during fall, winter and spring, when great temperature fluctuations can be expected. However, most tractor manufacturers recommend single-viscosity oils for heavy-duty service at temperatures above 320F., especially in diesels, because these oils are apparently less subject to deterioration and thickening under high temperatures than the multi-grades.
CD oils are required for fully-supercharged farm diesel tractors in high-speed heavy-duty operation and for some heavy-duty gasoline models.
Cooperative Extension Service PURDUE UNIVERSITY Lafayette, Indiana