The effect of methanol on the phase and phase-transition properties of a 2×8×8 glycerol-1-monopalmitate bilayer patch is investigated using a series of 239 molecular dynamics simulations on the 180ns timescale, considering methanol concentrations c M and temperatures T in the ranges 0–12.3M and 302–338K, respectively. The results in the form of hysteresis-corrected transition temperatures T m are compatible with the expected features of the biphasic effect, with a reversal concentration c rev of about 5.2M. Below this concentration, the main transition is between the liquid crystal (LC) and gel (GL) phases, and T m decreases upon increasing c M . Above this concentration, the interdigitated (ID) phase is the stable ordered phase instead, and T m slightly increases upon increasing T up to about 10M. The analysis of the structural and dynamical properties also reveals very different sensitivities and responses of the three phases to changes in c M . In particular, the properties of the GL phase are insensitive to c M , whereas those of the LC and ID phases are altered via an increase of the area per lipid. For the LC phase, increasing c M promotes disorder and fluidity. For the ID phase, in contrast, increasing c M up to about 10M slightly increases the ordering and rigidity. Two side issues are also addressed, concerning: (i) the occurrence tilt-precession motions in the GL and ID phases; (ii) the influence of the pressure coupling scheme employed in the simulations, semi- or fully-anisotropic, on the simulation results.