The ET23DC, also referred to as the SD23T4, is an EMD SD40-2 rebuilt by General Electric into an ET44AC variant. The aging EMD shells of these locomotives, instead of holding 16-645E3 prime movers as they were built, now have GEVO-6 prime movers, the first of their kind, under the hood, as well as the trademark cooling radiators. They are also equipped with Nathan K5HL air horns and Ekyrail E-bells. As of now, the only railroad that runs them is CSX, and they are numbered 1715-1727.
@TreeFan101 for the SD40-2 base @amtrakman4014 for the radiator (from an AC6000CW)