The ability to manipulate the liquid-liquid equilibria (LLE) of a commercially available hydrofluoroether (HFE-7100((R)), an approximately equimolar mixture of the isomers methoxy-nonafluoroisobutane and methoxy-nonafluorobutane) + water with the addition of ethanol, which is mutually miscible with both solvents, was examined. LLE data were determined at 298, 308 and 323 K for the system of HFE-71000((R)) + water + ethanol. The UNIQUAC and NRTL excess Gibbs energy models were able to adequately represent the type I phase behavior observed over this temperature range. The goodness of the fit of each model was compared for temperature-dependent and temperature-independent binary interaction parameters.