Texas & Pacific 4-8-2 "Mountain" Locomotives in the USA

The Texas & Pacific purchased five 4-8-2s (road numbers 900 through 904) from the American Locomotive Company in 1925. These "Mountains" were designated as Class M-1 and had 27 x 30 cylinders, 73" drivers, a 210 psi boiler pressure, a tractive effort of 52,500 lbs and weighed 360,500 pounds.

In 1928, another five 4-8-2s were delivered. This time, they came from the Baldwin Locomotive Works and were designated as Class M-2 and assigned road numbers 905 through 909. These locomotives were very similar to the Class M-1s except for an increase in total weight. Later, the boiler pressure of these last five oil burners was raised to 225 psi, which increased the tractive effort to 57,300 pounds.

There are no surviving T&P "Mountains".


ClassRoad NumbersYear BuiltBuilder

Class Details by Steve Llanso of Sweat House Media

Class M-1 (Locobase 229)

Data from T&P 1 - 1950ca Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange; and "4-8-2 Type Locomotives for the Texas & Pacific", Railway Age, Volume 80, #7 (13 February 1926), pp. 429-431. (Thanks to Chris Hohl for his 24 December 2021 email noting the original tender weight and capacities as well as supplying the link to the 1926 Railway Age report.) Works numbers were 66444-66448 in November 1925.

T&P Pacific type passenger engines couldn't quite muster all the tractive power needed for heavy main-line trains. So less than three years later, the railroad went to Schenectady for this quintet of Mountains, which offered "a boiler having ample proportions, a firebox of ample heating surface, total heating surface and volume, together with a feedwater heater [coil-type from Elesco] and superheater." The firebox included a long combustion chamber and two Nicholson thermic syphons of 70 sq ft (6.50 sq m). The specifications show just how ample were all of these components.

A Chambers front-end throttle mounted between the superheater header and the branch pipes regulated steam going to the 14" (356 mm) diameter piston valves that fed large, cast-steel cylinders.

Placing the cross-compound air pumps under the sidewise Elesco cylinder mounted ahead of the stack achieved "a satisfactory distribution of weight of the engine over the wheelbase. RA's report noted the placement of the whistle well forward, which "protects the occupants of the cab from the unpleasantness of having the whistle at close range, increases the effect of the whistle as a warning, and increases the volume and sharpness of the tone." (Trackside reaction to the whistle's decibel output didn't feature in the report.)

Chris Hohl noted that the onginal tender capacities amounted to 12,000 US gallons (45,240 litres) of water and 5,000 gallons (18,925 litres) of oil for a loaded weight of 259,000 lb (117,481 kg).

The Baldwin engines of 1928 had some slight differences; see Locobase 8511.

Al1 ten 4-8-2s handled the long-haul passenger trains such as the Sunshine Special, the Texan, and the Southerner.

Class M-2 (Locobase 8511)

Data from T&P 1 - 1950ca Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to John B Price for his 9 June 2016 email correcting the feedwater information.) See also DeGolyer, Volume 80, pp. 664+. Works numbers were 60551-60555 in July 1928.

The first five Mountains procured for passenger service by the T & P came from Schenectady in 1926 (See Locobase 229). The current entry describes the later five that arrived three years later. Like the M-1s, the M-2s had fireboxes whose heating surface area included 119 sq ft (11.05 sq m) in the combustion chamber and two Nicholson Thermic Syphons adding 70 sq ft (6.5 sq m).

The Walschaert valve gear operated 14" (356 mm) piston valves with 8" (203 mm) travel. Unlike the M-1s, which had Elescos, the M-2 boiler was fitted with the Coffin C-80 feedwater heater. The differences between the two classes were admittedly small: a slight increase in grate area and, consequently, in firebox heating surface and a more substantial reduction in superheater area.

Al1 ten 4-8-2s handled the long-haul passenger trains such as the Sunshine Special, the Texan, and the Southerner. The T & P was an early adopter of an all-diesel motive-power roster and the last steam run of any sort came in 1951.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID229 8511
RailroadTexas & Pacific (T&P)Texas & Pacific (T&P)
Number in Class55
Road Numbers900-904905-909
Number Built55
Valve GearWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)20 / 6.1020 / 6.10
Engine Wheelbase (ft / m)43.25 / 13.1843.25 / 13.18
Ratio of driving wheelbase to overall engine wheelbase 0.46 0.46
Overall Wheelbase (engine & tender) (ft / m)84 / 25.6084 / 25.60
Axle Loading (Maximum Weight per Axle) (lbs / kg)61,400 / 27,85161,500 / 27,896
Weight on Drivers (lbs / kg)245,500 / 111,357245,600 / 111,402
Engine Weight (lbs / kg)360,500 / 163,520361,400 / 163,928
Tender Loaded Weight (lbs / kg)280,100 / 127,051291,666 / 132,298
Total Engine and Tender Weight (lbs / kg)640,600 / 290,571653,066 / 296,226
Tender Water Capacity (gals / ML)14,000 / 53.0314,000 / 53.03
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)6000 / 22,7106000 / 22,710
Minimum weight of rail (calculated) (lb/yd / kg/m)102 / 51102 / 51
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 185473 / 1854
Boiler Pressure (psi / kPa)210 / 14.50225 / 15.50
High Pressure Cylinders (dia x stroke) (in / mm)27" x 30" / 686x76227" x 30" / 686x762
Tractive Effort (lbs / kg)53,477 / 24256.7957,296 / 25989.06
Booster (lbs)10,20010,450
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.59 4.29
Heating Ability
Tubes (number - dia) (in / mm)175 - 2.25" / 57175 - 2.25" / 57
Flues (number - dia) (in / mm)43 - 5.5" / 14043 - 5.5" / 140
Flue/Tube length (ft / m)20.50 / 6.2520.50 / 6.25
Firebox Area (sq ft / m2)404 / 37.53409 / 38
Grate Area (sq ft / m2)80.30 / 7.4681.12 / 7.54
Evaporative Heating Surface (sq ft / m2)3768 / 350.063774 / 350.74
Superheating Surface (sq ft / m2)1110 / 103.121032 / 95.91
Combined Heating Surface (sq ft / m2)4878 / 453.184806 / 446.65
Evaporative Heating Surface/Cylinder Volume189.54189.84
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16,86318,252
Same as above plus superheater percentage20,74122,085
Same as above but substitute firebox area for grate area104,353111,350
Power L120,27820,803
Power MT728.40746.95

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