An interim model between the very successful SD40-2 series and the later 710-powered SD60 and SD70, the SD50 would not have the sales of the preceding SD40-2; indeed, the earlier locomotive was kept in production for US customers for much of the SD50’s run, and indeed Canadian and Mexican orders for 40-2s were being fulfilled long after the SD50 line had been shut down.
The SD50 production versions had longer frames than the Dash-2s, but six prototype SD50S models were shorter, these ending up with Norfolk & Western (later Norfolk Southern). The 645 powerplant was upgraded to 3,500hp (3,600 in later units) but this was asking too much of the design, and led to reliability issues., in addition to electrical problems also encountered with the SD50s.
CSX inherited SD50s from B&O, C&O, Conrail and Seaboard; 8600 is a former SCL unit. Some CSX units (including 8600) were derated to 3,000hp as SD50-s, while just over a dozen units were derated, given microprocessor controls, and new control stands as SD50-3s.
Many SD50s were purged from the CSX roster starting in 2018, including 8600, which went to LTEX Rail.