Only 6 were officially built, while a seventh cab from an unbuilt MK5000C was used in a rebuilt SD45, known as an SD50M.
The MK5000C was one of the first North American 12-cylinder diesel locomotives to contain a DC-traction 5,000hp engine (as opposed to the AC-traction 5,000hp EMD SD80MAC produced a year later in 1995), with only 6 built, all for MK's lease fleet. Three units were painted for SP, on long term lease the other three were in MK paint and tested on the UP. They were very successful with their performance at first; having a smooth, even ride while hauling heavy coal trains during test runs. However, they were very expensive to manufacture and often had engine troubles and numerous other mechanical failures (besides the unusual cab design being disliked from most crews). Morrison Knudsen (unfortunately) declared bankruptcy in the 1990's as a result of the MK5000C's unsuccessful run, and subsecquently the Wabtec Corporation purchased the company ceasing production of the MK5000C due to being unpopular with railroads, and the Southern Pacific ultimately purchasing a large fleet of GE's introduction of their ever-popular AC4400CW (which completely dominated over EMD's SD70MAC and subsequently: the MK5000C) and thus cancelling the mass-production order of 50 MK5000C's to replace their aging EMD "Tunnel Motor" Series (SD45T-2 and SD40T-2) of diesel locomotive types.
All 6 units are now in service on the Utah Railway, and operate on former Southern Pacific lines, but are now fitted with former UP EMD 16-645 prime movers (All 6 from EMD SD50 units,replacing the 5000hp Cat 3612 type of engine; which was plagued with mechanical issues.
After years falling coal prices forced Utah Railway to sell the units in 2017. On March 16th 2017 all of the units except 5003 and 5007 left Utah Railway's yard in Martin for the last time after a final run up Soldier Summit. The locomotives were then shipped East on the BNSF Railway and sold to Kyle Railway in Denver Colorado. Kyle is trading them for Alcos which will then be sold to SMS Rail Lines in Camden New Jersey. On the morning of March 31st and April 6th 5003 and 5006 left Utah for the last time and both trains arrived in Denver 4 days later to join their kin.
- The MK5000C is also known as simply the "MK50" or, "MK50C".
- The MK5000C is one of the first diesel locomotives to be built with a Caterpillar engine. (With it being the CAT V12.)
- The MK5000C is also the very last locomotive to have been produced by MK Rail before being purchased by Wabtec and becoming MotivePower Industries.