Comparison of the Physical and Chemical Changes Occurring in Oils During Aging in Vehicle and Engine Fuel Economy Tests

Oils, which do not contain Molybdenum (Mo)-based friction modifiers, were aged in vehicle and engine fuel economy tests in order to determine if the different aging protocols caused similar changes in the physical and chemical properties of these oils. Vehicle and engine tests were found to cause similar changes in the high temperature high shear (HTHS) viscosities and boundary friction coefficients of oils. We also observed that the extent of oil oxidation, nitration and volatilization occurring in the vehicle tests could be duplicated by aging in the engine tests. The fuel economy performance of aged oils was also measured in engine tests and found to be highly dependent upon the aged oil's HTHS viscosity. However, we observed that an aged oil's boundary friction coefficient, by itself, did not correlate to an aged oil's fuel economy performance in the high temperature fuel economy measurement stages of engine tests.