Abstract The current situation of the oil industry and the recurring change in oil prices has prompted companies to look for alternatives to reduce their operating costs and investments without affecting their operations or production. Under this context, an Ecopetrol operation in Colombia's has decided to use an existing well to convert it into an injector well using a modified Electro-Submersible Equipment (ESP) as a pump injector, so this will result in an "inverted" installation compared to a conventional one. This project represented different challenges in the completion; one of them was, because the impossibility of using a conventional ESP sensor, to estimate the internal temperature of the downhole motor, from variables measured both in surface and in the depth of the equipment installation. Knowing the motor temperature is important considering that it is necessary to ensure system reliability and set the operating limits of the equipment. For this application, the use of a zenith C6 downhole sensor (which does not measure the internal motor temperature) was considered, and software was developed capable of estimating it from other variables measured in the surface and in the downhole. The results were contrasted with the company's official equipment design and selection software, obtaining values with an error within an acceptable range. The "inverted" ESP equipment was not installed to date, but it is estimated that the installation should take place in the coming months.