International regulations on the reduction of fuel consumption and CO2 emissions to the atmosphere have made the transportation industry in general, and the automotive in particular, to look for the improvement of aluminium alloys used in manufacture of internal combustion engines. Smaller and lighter engines able to develop higher power outputs rely on increasing the temperature within the combustion chamber, which imply augmenting thermal and mechanical demands of the alloy used in the manufacture of powertrain components. Al-Si alloys are used due to their combination of low density, high strength and the feasibility of attaining complex shapes. Such strict demands require the design of newer engines able to dissipate the heat generated within the combustion chamber to avoid the damage that higher temperatures may cause to the alloy. The work conducted on cast aluminium-silicon alloys to evaluate their thermal diffusivity dependence with respect to temperature, chemical composition, microstructure and heat treatment imparted are presented in this work. The results show how thermal diffusivity can be enhanced by adequate design and proper heat treating practices imposed to the alloy.