The present invention relates to a method of preparing a stable and well-dispersed ZnO-EG/DW based nanofluid that utilizes ethylene glycol and distilled water without the use any kind of surfactant, dispersing and stabilizing agent. The method includes the steps of diluting a zinc acetate precursor in a blend of ethylene glycol and distilled water solution as a first solution; mixing a strong base sodium hydroxide in ethylene glycol-distilled water mixture; ultrasonicating the mixture to obtain a reaction mixture; separating zinc oxide (ZnO) nanoparticles by washing, drying and calcination; and dispersing ZnO spheres in ethylene glycol-distilled water solution to obtain zinc oxide-ethylene glycol/distilled water (ZnO-EG/DW) nanofluid.