Ferrofluids are a unique class of colloidal liquids made of ferromagnetic or ferrimagnetic nanoparticles suspended in a carrier fluid. Ferrofluids have drawn considerable attention due to the possibility of tuning their heat transfer and flow properties through the application of an external magnetic field. They can also be utilized to improve the performance of an energy harvester, which can supply power and enhance the capability, assertion and lifespan of those devices where batteries or direct electricity are currently used as the primary source of power. Electromagnetic ferrofluid based energy harvesters convert the ferrofluids sloshing movement into electromotive force; therefore, it is necessary to estimate the feasibility, stability and efficacy of ferrofluids through several physicochemical studies. The objective of this work is to prepare a stable polymer coated Fe3O4 nanofluid with the aim of applying it in a novel energy harvester device currently under development at the University of Newcastle. The one-step chemical precipitation method was complied with to produce Fe3O4/DI-water nanofluids, and thermogravimetric analysis and differential thermal gravimetry have been carried out to determine the chemical and physical changes of ferrofluids due to thermal effect. Besides, X-ray diffraction was employed to identify the crystal structure. The stability and physicochemical properties of Fe3O4 particles were also investigated. The synthesized ferrofluids were found to be visually stable for more than 2 months. The results showed that the synthesized nanoparticles were magnetite, and a linear relationship was found among the dosing rate of ammonium hydroxide, nanoparticle size distribution, viscosity and thermal conductivity. Higher dosing rates of ammonium hydroxide reagent during the preparation of nanoparticles resulted in increasing average particle size.