In this experimental and statistical investigation, Silver (Ag) nanoparticles with varying particle sizes of 20 nm with the base fluid of EG and DI water are tested to improve the heat transfer properties of the car radiator. The thermophysical properties are tested at temperatures varying from 35 to 75 °C. Results showed that small nanoparticles had higher thermophysical properties than large nanoparticles. The heat transfer properties along with friction factor characteristics are measured. A total of 20 nm of Ag has higher thermal transfer properties than other nanofluids; it can be concluded that smaller nanoparticles can improve thermal properties and minimize the radiator size compared to traditional coolants. A systematic optimized RSM-based architecture has been developed to define the quantitative estimate of the specific design parameters influencing nanofluid heat transfer properties and friction factor …