Conventional fluids, such as water (W), ethylene glycol (EG) and mixture of them (W/EG), are usually used as heat transfer fluids. Their poor heat transfer rate is an obstacle for enhancing efficiency of heat exchangers. A novel type of fluids called “nanofluids” (NFs) is recognized for improving the performance of heat transfer fluids. NFs are two phase fluids where solid nanoparticles (NPs) are dispersed in base liquids, which are expected to enhance the heat transfer properties of traditional fluids by improving their thermal conductivity (TC). In the last decade, NFs have achieved considerable attention due to their enhanced thermal conductivity. Mainly two methods are used to fabricate NFs: the two-step method wherein first NPs are synthesized and then dispersed in the conventional heat transfer fluids, while in the one-step method NPs are formed directly inside the base liquid. Due to large scale availability of commercial NPs, two-step method is the most commonly used technique. However, some issues such as presence of impurities or undesired phase on commercial NPs may influence the thermo-physical properties of NFs including TC and viscosity. In fact, making commercial NPs without any impurities is almost impossible and removal of undesired phases from the commercial NPs with no negative impact on NPs composition is also difficult. Hence, to study the real contribution of NPs on thermo-physical properties of NFs we performed a systematic experimental work using commercial SiC NPs with both α- and β crystal structure and silica (SiO₂) NPs as secondary phase to make SiC/SiO₂ composite material. The reason for selecting SiO₂ is due to our recent findings on commercial α- and β SiC NPs where analysis on NPs, particularly β phase, showed silica impurity phase. Presence of this impurity/undesired phase does not reflect the real heat transport property of SiC NPs. Thus we focused on fabrication of SiC/ SiO₂ composite material with different structures including core-shell structure (presence of silica phase as shell), functionalization of SiC NPs with SiO₂ phase as well as addition of different percentage of SiO₂ to SiC NPs as secondary phase. The obtained composite materials were used to fabricate W/EG based NFs with 9wt% NP concentration. Physicochemical properties of NPs/NFs were characterized by using various techniques. The thermo-physical properties of NFs including TC and viscosity were measured and analyzed at 20 ^oC. Our findings and results obtained from physico-chemical, thermo-physical and heat transport characteristics are presented in detail.