This study investigates the effect of a magnetic field on the thermal properties of ethylene glycol and water-based Fe3O4 magnetic nanofluids. To make a magnetic nanofluid an option, the magnetic field strength and concentration of the magnetic nanoparticles should be optimized. This was achieved in a small-scale laboratory system designed to simulate the cooling cycle of an internal combustion engine, which was exposed to a constant magnetic field. The concentrations of the magnetic nanoparticle in the Fe3O4 nanofluid ranged between 0.025% and 0.2% by volume. The mean sizes of nanoparticles were 20 -30 nm. The research used a consistent magnetic field of 0.05,0.10, and 0.15 Tesla. The thermal properties that have been studied are the heat transfer coefficient, thermal conductivity, heat transfer rate, and Nusselt number. Experimental results indicate that the thermal properties of the Fe3O4 magnetic nano fluids were enhanced under an applied external magnetic field. The effect of the magnetic field is strongly dependent on the concentration of magnetic nanoparticles in a mixture of ethylene glycol/water. The thermal properties significantly improved at a magnetic field strength of 0.15 Tesla when using a concentration of 0.2 vol.% nanoparticles. This led to a maximum increase of 18.4% in the heat transfer coefficient. At this volume fraction and with the 0.15 Tesla magnetic field, the thermal conductivity increased by 8.22%. Additionally, the most significant increase in the Nusselt number was observed at a Reynolds number of 7500 under the same magnetic field conditions.