Due to design differences, it would not be possible to use the same type of diesel engine across all locomotives, and so two different types were selected:  The process was spread out from the late 1970s into the early 1980s. As part of this, some locomotives were repainted in the International Orange livery but with their pre-TMS numbers instead of the later TMS numbers. As a result of this, the locomotives were equipped with new radiator header tanks which were mounted behind the radiator on top of the engine hoods in a 'north-south' alignment. Later the tanks were relocated to an 'east-west' alignment. The introduction of the Traffic Monitoring System (TMS) in 1979 saw the locomotives renumbered. In 1989, DSC 2406 was trialled as the first shunting locomotive to be fitted with shunter's refuges at either end of the locomotive. New recessed steps were fitted at either end of the locomotive frames with a vertical hand-rail on the running-board proper. The locomotive's engine hoods were not shortened at the time. This modification was successful, but it was noted that the engine hoods were a potential constraint. All further DSC class locomotives equipped with the refuges had their engine hoods shortened by 500mm, necessitating the relocation of the radiator header tanks to their present 'east-west' alignment. This modification was subsequently made to all DSG, DSJ, and DH class locomotives as well as DAR 517. None of the BTH-built DSC class locomotives were fitted with these refuges and several NZR-built examples did not receive them either, due to withdrawal before they could be fitted or by dint of being used for other purposes. As of September 2018, 42 units have been withdrawn from service. As a part of the program of the New Zealand Railways Corporation to rationalize the locomotive fleet in the late 1980s, all of the British Thomson-Houston built locomotives were withdrawn. All, besides one, were scrapped either at Otahuhu Workshops, or at Hutt Workshops between October 1989 and early 1990. DSC 2067 was given a reprieve when it was sold to the NZ Dairy Group (later subsumed into Fonterra) to shunt their Whareroa milk factory. In 2003, the loco was overhauled at the Westfield servicing facility. The overhaul included repairs and a repaint.