Helically coiled tubes find applications in various industrial processes like solar collectors, combustion systems, heat exchangers, and distillation processes because of their simple and effective means of enhancement in heat and mass transfer. Though extensive work is available in the literature on curved tubes, no study is available considering the variation in thermo-physical properties of fluids (density, viscosity, thermal conductivity, and specific heat) with temperature. In the present work, the effect of temperature dependence of fluid properties is examined on both hydrodynamic and thermal performance of the curved tube having finite curvature and pitch, under cooling and heating conditions. The range of Reynolds number studied in the present work is varied from 100 to 400 using water and diethylene glycol as two different fluids. The secondary flow induced due to centrifugal force distorts the velocity and temperature profiles when the effect of temperature-dependent properties is taken into account. The friction factor obtained with variable property assumption under cooling is higher as compared to the constant property results. This is due to the increase in the value of viscosity near the wall of the curved tube that reduces the effect of the secondary flow. The Nusselt number also shows a marked dependence on the properties variation in the coil tube cross section. A new model is also developed in the present study based on the property-ratio technique for both friction factor and heat transfer. The study provides understanding of the fundamentals of energy transportation in curved ducts and will be very helpful in designing coiled tube heat exchangers with temperature-dependent properties.