PRR 3750 was used to haul the Pennsylvania Railroad's main line passenger trains such as the Broadway Limited. Despite the attempt by railroad management to replace the K4s with the K5 and T1, the K4s would remain in action until dieselization in 1957. The 3750 was spared from being scrapped because, when the Pennsylvania Railroad was considering steam engines for preservation, the first K4, 1737, had deteriorated to the point that it was not worth preserving. The Pennsylvania decided to scrap 1737 and use 3750 as a stand-in; 3750 received the original number plates and tender from 1737.
In 1921, 3750 headed up soon-to-be President Warren G. Harding's campaign train. Three years later, it also was one of the locomotives that pulled Harding's funeral train.
The Pennsylvania General Assembly designated 3750 and 1361 the official state steam locomotives on December 18, 1987, while also designating the GG1 4859 the state electric locomotive in the same bill.
As of 2008, the 3750 sits on static display at the Railroad Museum of Pennsylvania in Strasburg.