Solid-liquid and liquid-liquid equilibrium temperatures for mixtures of 1,3,5-trioxane, or 1,4,7,10,13,16-hexaoxacyclooctadecane with n-heptane, or with n-tridecane, or with n-hexadecane are reported. The equilibrium temperatures were measured by a dynamic method. Mixtures with n-tridecane, or n-hexadecane show a eutectic point. 1, 4 7.10.13.16-Hexaoxacyclooctadecane present a transition point in solid phase, which depends on the solvent. Dipole-dipole interactions are stronger in solutions with 1,3,5-trioxane. Mixtures were investigated in terms of DISQUAC and the corresponding interaction parameters are given. The model describes in the correct range of temperature and composition the coordinates of the eutectic and critical points. The influence of proximity effects and cyclization on the interaction parameters is discussed. So, proximity effects are found to be important for interaction parameters of systems involving crown ethers. Departures from the observed behavior of the interaction parameters for solutions with more simple oxaalkanes are ascribed to the existence of liquid-liquid equilibria in the studied solutions.