Diesel of the Day BONUS: K-M ML-4000

Because it’s August 1st and I am still Goat as of now, you all get a bonus DotD: the Krauss-Maffei ML-4000. This is quite an unusual diesel in very many ways. It was ordered by only three railroads, the Southern Pacific, the Denver & Rio Grande Western, and EFVM in South America. 37 were built between 1961 and 1969. The ML-4000 is what’s known as a diesel-hydraulic locomotive. Unlike a standard diesel-electric, in which a diesel engine drives an electric generator powering traction motors, a diesel-hydraulic’s engine turns a large hydraulic pump, which rotates the wheels. This technology is much more common in Europe, and is largely obscure in North America. The builder, Krauss-Maffei, is based in Germany, and the ML-4000 was, to my knowledge, their only foray into US locomotives. This unit is powered by a pair of Maybach MD870 high-speed four-stroke turbocharged V16 engines producing 1,770 horsepower each, for a total power output of 3,540 horsepower. The engines sent power to the hydraulic pumps above the trucks via a pair of Cardan shafts (driveshafts). Two different variants were produced, one with a full-width carbody and one with a more standard cab and walkways. These units were not particularly successful despite their high horsepower, and shop crews had to be specially trained (or in some cases, imported!) to perform maintenance on the unfamiliar European engines and components. Of the original production run, only one unit, Southern Pacific number 9010, has been preserved, and work is ongoing. This unit has an interesting backstory, and is worth a read if you have some spare time. The photo this time shows one of SP’s ML-4000s with the full-width cab and body in service.