155 locomotives were rebuilt by the Seaboard Coast Line. The vast majority of them came from Atlantic Coast Line, Seaboard Air Line and their subsidiaries ; 8 units came from Clinchfield Railroad, not counting the six units rebuilt at Paducah ; seven units came from Louisville & Nashville. The required modifications took nine weeks per unit on average to complete. The rebuild work was done at the railroad's Uceta Shops near Tampa, Florida, with the engines, bogies and traction motors rebuilt at Waycross and Jacksonville. The program resulted in a cost savings of almost 50% over buying new locomotives. Included in the program:
Rebuilding the underframe assembly;
Remanufacturing the Blomberg B two-axle trucks, generators, and traction motors ;
Replacing the existing 567prime mover with a new EMD 645 series diesel engine, which boosted the horsepower rating to 1,600 in the case of the former GP7 locomotives. This gave rise to the 16 designation.
Lowering the front nose of the carbody to improve visibility, and retrofitting with a new cab and standard AAR control stand.
Ancillary benefits included a lowered engine idling speed and increased fuel efficiency. SCL committed over 100 of its personnel to the conversion program. The first GP16 emerged from SCL's Uceta shop in June 1979 while the last was placed into service during November 1982.
In service
The rebuilt locomotives saw service throughout the system, engaging in a variety of duties from local switching to main-line freight hauling. Though SCL became part of the CSX Transportation system in the 1980s, the majority of the units remained active until 1992, when the bulk of the roster was retired and sold-off. Many GP16s remain in active service today on short line railroads around the country, far exceeding their 15-year projected lifespan. In 1993 the U.S. Army bought a small number of GP16s from CSX, which led some people to think the Army built it. The locomotives were sent to Conrail's Juniata Locomotive shops to be 'remanufactured' under contract with the Army. When they were completed, Conrail put a GP9M plate on them. These locomotives are controlled by Woodward PGR type diesel engine governors.
Other units called GP16
In the late 1960s through the early 1970s, the Missouri Pacific Railroad repowered their entire roster of high-hood ALCO RS-11s with EMD 567 series diesel engines. These converted units were designated by the MP as "GP12s" and "GP16s" presumably to reflect their new horsepower rating.
Clinchfield Railroad had six GP7s rebuilt by ICG Paducah and they were called GP16s, but built to the same standard as ICG GP11s. When the CSX merger occurred these engines were grouped as GP16s. Two notable features was the angled cab and air intake filters.
