The cooling performance of a prototype immersed coil with magnetic fluid is evaluated in this paper, in order to estimate the heating process in a power transformer. For this purpose, thermocouples are inserted at several positions in the experimental setup. A magnetic fluid (Midel vegetable oil-FeCo2O4 Cobalt ferrite magnetic fluid) with nanoparticles volume fraction of 7% is used to improve cooling efficiency. The impact of a radial ring magnet located close to the ferrofluid tank is studied. The magnetic suspension proposed for solenoid cooling is influenced, in addition of the heat source magnetic field, by the magnet location around the tank. The temperature reduction in the coil, due to thermomagnetic convection, has been already assessed in a previous study. Experimental results match with numerical ones performed with a 2D axisymmetric model of the setup, using the finite element method. It is shown hence that the magnet reinforces the temperature decrement.