Mineral oil has been serving well as a cooling and insulation oil in high voltage power equipment but with a setback when considering environmental friendliness whenever there is spillage due to its poor carbon profile. Several works have been done on the enhancement of dielectric properties of green alternative with different nanoparticles but little attention was placed on its cooling properties which is one of the major functions of the oil. Also, to prevent food competition, esters from a non-edible seed oil should be given more consideration. This work, therefore, investigates the cooling properties of synthesized insulating nanofluid using Neem oil ester as the base fluid together with (Insulating) SiO₂ and (semiconductive) WO₃ nanoparticles. The nanoparticles were characterized using FTIR and XRD to confirm their functional groups and crystallite size respectively. Transesterification of the oil was done using sodium methoxide and the nanofluid samples were prepared by dispersing the nanoparticles into the oil. The nanoparticles were varied from 0.2 wt% to 1 wt%. The pour point, flash point and viscosity were measured according to ASTM standards. An increase in the pour point, flash point and viscosity were observed at every loading of the nanoparticle. The nanofluid with dispersed SiO₂ nanoparticles were observed to possess superior properties as a cooling liquid in high voltage power equipment when compared with the fluid with WO₃ nanoparticles because of its low viscosity, low pour point and good flash point. After the ageing, the synthesized fluids still retained their properties which is better than the mineral oil.