Vapor pressures, phase equilibria and interfacial tensions sigma were measured for solutions of poly(dimethylsiloxane) (PDMS, M-w = 75 kg/mol and M. = 50 kg/mol) in mixed solvents of toluene (TL) and ethanol (EtOH) at 30, 40, 50 and 60 degreesC. The experimental ternary phase diagrams can be modeled quantitatively from the determined concentration and temperature dependent binary interaction parameters chi(ij) if the experimentally inaccessible composition dependence o chi(EtOH)/(PDMS) is adjusted. The relations between o, and the equation of state of the system differ from that applying to single solvents. The exponents as well as the amplitude prefactors of the corresponding scaling laws (e.g. the dependencies of o, on the length of the tie lines or on the hump energy, i.e. on the intrusion into the two phase regime quantified in terms of Gibbs energies) change considerably with temperature. However, this variation can be reduced significantly by normalizing the independent variables. Dividing the length of the tie lines by the length for the corresponding binary subsystem proves more efficient than the distance of these tie lines from the critical point of the ternary system relative to the maximum distance of the binary subsystem. A combined normalization does not improve the situation.