A method based on apparent viscosity of engine oils at 0°F measured by the cold cranking simulator to estimate minimum starting temperatures for SAE “W” numbered engine oils is described.
Based on apparent viscosity measurements, a nonpolymer-containing SAE 20W-30 engine oil would satisfy 100% of gasoline or diesel engine powered fleets where temperatures are consistently above 0°F. Based on climate and vehicle distribution by geographical location, about 15% of gasoline engine powered vehicles require engine oils with low-temperature properties found in SAE 5W or SAE 10W engine oils. Diesel engines using a nonpolymer-containing SAE 20W-30 engine oil would obtain the benefits of SAE 20W low-temperature starting properties and SAE 30 high-temperature protection.
Initial field tests of gasoline-powered vehicles in severe winter service indicate adequate low-temperature properties for a nonpolymer-containing SAE 20W-30 engine oil compared to an SAE 20W-20 grade normally used in this application in winter. This method may also be used to compare low-temperature properties of engine oils containing different V.I. improvers.