The article is dedicated to the currently important problem of increasing the efficiency of cooling systems of oil transformers with considerable long and short overloads. Increasing the efficiency of cooling in oil transformers makes it possible to increase their engine life, improve efficiency and safety of operation. Statistical data are given on the causes of failure of the transformers of different voltage classes and with different operating times. Based on the study of statistical data, it is established that inefficiency of oil cooling systems during the summer period of operation and with considerable short overloads is one of the main causes of transformer failure. To increase the efficiency of cooling systems of oil transformers, we propose agitation of cooling oil with circulating sulfur hexafluoride and subsequent cooling of sulfur hexafluoride with a thermoelectric cooler. The system of circulation and cooling of sulfur hexafluoride switches on automatically with considerable long and short overloads. We have considered the design and operation of the proposed cooling system for oil transformers. A series of laboratory experiments was carried out for cooling transformer oil in a power transformer tank with and without a compressor. The temperature versus time curves have been plotted for natural cooling and for the case when agitation is used. We have experimentally determined the coefficients of thermal diffusivity and heat transfer of transformer oil at various distances from the heating element. We have considered the mathematical problem of the distribution of the heat flux in a rectangular parallelepiped and obtained the solution of the heat conduction equation in a tank of a power transformer shaped as a rectangular parallelepiped. The construction of a laboratory installation is described in detail. The brands of thermocouples used, the brand of the compressor and the analog-digital converter are given.