This study presents a systematic experimental evaluation of the thermal and rheological properties of Behran oil-based nanofluids formulated with three inexpensive and easily synthesized nitride nanoparticles: boron nitride (BN), carbon nitride (CN), and boron carbon nitride (BCN). Each nanoparticle was surface-functionalized to improve dispersion stability and dispersed at concentrations of 0.1–0.5 wt.%. Thermal conductivity, convective heat transfer coefficient, specific heat capacity, and viscosity were measured at 25 °C, 35 °C, and 50 °C. Structural and morphological characteristics of the nanostructures were confirmed through FTIR, XRD, SEM, TEM, and DLS analyses. The nanofluid containing BN showed the highest thermal conductivity enhancement (14.92% at 0.3 wt.% and 50 °C), while CN led to the greatest increase in specific heat capacity (414% at 25 °C). BCN exhibited moderate enhancements across both properties. All nanofluids exhibited minimal viscosity increases (< 1% at 50 °C), suggesting their potential suitability for high-performance thermal systems. These results highlight the potential of functionalized nitride nanostructures as effective additives for improving the heat transfer performance of industrial lubricants.