Metal matrix nanocomposites encompassing low-melting point metal nano-inclusions are promising candidates for thermal regulation of devices at high temperature. They are usually processed by solid-state routes that provide access to a limited range of materials and are hardly compatible with complex shaping processes and with large-scale applications. Herein, we develop a liquid-phase processing technique to design aluminum matrix nanocomposites made of phase change nanoparticles, using bismuth nanoparticles as a proof-of-concept. The bismuth nanoparticles derived from colloidal chemistry are first encapsulated in a silica shell and then dispersed by ultrasonication into molten aluminum. Using X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy, we probe the evolution of the bismuth particles and of the inorganic shell. We demonstrate that the silica shell acts as a barrier against extensive coalescence of particles during the dispersion process, thus enabling a decrease and a widening of the phase change temperature range.