After studying engineering in Edinburgh, Scotland, and returning home to Canada, he found work as a fireman and oiler at the Michigan Central Railroad. In a home-based machine shop in Ypsilanti, McCoy invented an automatic lubricator for oiling the steam engines of locomotives and boats. For this he obtained his first patent, "Improvement in Lubricators for Steam-Engines" (U.S. Patent 129,843 ) on July 23rd, 1872. Similar automatic oilers had been patented previously; one is the displacement lubricator which had already attained widespread use and whose technological descendants continued to be widely used into the 20th century. Lubricators were a boon for railroads, allowing trains to run faster and more profitably with less need to stop for lubrication and maintenance.

Other inventors tried to copy McCoy's oil-dripping cup. But none of the other cups worked as well as his, so customers started asking for "the real McCoy." That's where the expression comes from.