The paper examines the influence of dispersion of multi-walled carbon nanotubes on the thermo-physical properties of working fluids used in solar thermal engineering systems. Thermo-physical property evaluation is very vital to evaluate the performance of solar thermal systems. Ethylene glycol and a commercially reachable thermic fluid therminol 62 are preferred as based fluids. Nanofluids are prepared by dispersing 0.1 %, 0.25 %, 0.5 % and 0.1 % weight fraction of surface modified Multi-walled carbon nanotubes. The nanomaterials are surface modified before dispersion in the thermic fluids and extreme care is taken to prevent property deterioration during surface modification. Thermal conductivity of test fluids is evaluated in the temperature range of 100 to 300°C while viscosity is evaluated in the range of 50 to 150°C s. A 15 to 20 % increase in the thermal conductivity is observed with the dispersion of carbon nanotubes. The viscosity is significantly increased in the low-temperature ranges while the change is minimal above 70. The data could be predicted successfully using artificial neural networks.