The use of ethanol as an additive to gasoline fuel is becoming a common phenomenon. It helps solve the energy crisis and environmental issues that fossil fuel has brought about. However, when dissolved in motor oil, ethanol would dilute motor oil and drastically change its lubrication properties, in the same manner as gasoline dilution. Since ethanol has higher boiling point than gasoline, it takes longer time to be cooked away from the oil, causing more severe changes to motor oil properties. In this work, a new analytical method is presented to study the behaviour of ethanol/oil system. Seven motor oil formulations provided by Italian group E.n.i. are tested regarding their performance in resisting ethanol dilution. The tests are conducted in microcapillaries within which ethanol droplet dissolves in motor oil phase under 40oC or 60oC. Mathematical model is developed to study the shrinkage kinetics of ethanol droplets. And, the mass transfer coefficients of ethanol transporting to different oil formulations are obtained. Similar experiments are conducted on hexadecane and new and used Shell SAE 5W-30 motor oil to discover the difference between motor oil and pure hydrocarbon and the difference between new motor oil and used motor oil. It was found through hexadecane tests and Shell motor oil tests that hydrocarbons with shorter chain length were less capable of resisting ethanol dilution; old motor oil are slower in dissolving ethanol than new oil; and, suspected ethanol-soot complex may form in old motor oil, which might corrode engine parts. / acase@tulane.edu