Solvent-free extrusion emulsification (SFEE) is a new continuous approach for producing nanoparticles from high viscosity molten polymers using a twin-screw extruder. In a previous study, the influence of melt viscosity on lamellae development in the phase-inversion mechanism was investigated for an otherwise fixed system of variables including temperature, mixing intensity, and surfactant content. Varying system temperature in the current study to produce the same melt viscosities as those previously examined did not produce the same linear effect on particle size. The investigation to understand the influence of system temperature on the SFEE mechanism was done by using an inline rheometer and different screw/barrel configurations to simulate different zones of SFEE. Characterizations of the emulsified polyester included colorimetric titrations, particle size analysis, parallel plate rheometry, and gel permeation chromatography (GPC). Raising system temperature has a negative effect on the mechanism for producing smaller particles, countering the positively affected parameters, namely lower melt viscosity and a higher content of surface active species based on a contributing neutralization reaction. The findings show good fit to published studies of an osmotic pressure-driven emulsification mechanism, which is beneficial in clarifying the role of surfactants in the process. Overall, the results show system temperature to be a complex variable in SFEE, deeming it undesirable in optimizing the process.