Southern Pacific experienced problems with locomotives overheating in tunnels. This brought about a major design change in the new SP SD45-2s.

The traditional EMD sidemounted radiators and roof fans were replaced with roof-mounted radiators, internal fans and a large opening at the bottom of the rear of the long hood. This allowed for cooler air to be pulled upward through the radiators.

The new locomotive was nicknamed “Tunnel Motor,” both for the problem it addressed and the opening in the long hood. While SP initially bought the SD45T-2, Rio Grande chose the 3000-horsepower SD40T-2. SP also purchased a large numbers of SD40T-2s.

Today, both SP & D&RGW are gone, absorbed by Union Pacific. But the Tunnel Motors remain, many serving on Class II roads and short lines across North America. And just like the SD40-2's these will continue to work the rails for many years to come.

Starting in the 1990s, Kansas City Southern turned to second-hand locomotives to meet its needs. This included seven SD40T-2s from Union Pacific acquired in 2001. The SD40T-2s 6100 and 6104 were built as Southern Pacific 8524 and 8523 in December 1978. Built as SP 8237 in April 1980, number 6107 features an exhaust silencer and bulged dynamic brake blister, the result of noise-reduction regulations.

General Model Features:

• See-through radiator intake grilles
• See-though exhaust stack
• Snowplow and/or MU catch boxes
• MU hoses
• Coupler cut bars
• Dynamic or non-dynamic brake
• Minimum radius: 18”
• Recommended radius: 22”
• DCC Ready
• Ex-Southern Pacific units
• 88” nose with brake wheel, no headlight
• Non-operating ditch lights
• Breakaway stanchion on the end handrails
• Modified L-windshield
• Cab-side vent
• Large SP-style snowplows
• 4500-gallon fuel tank—4400-gallon tank with an internal 100-gallon retention tank
• Double fuel fills
• Ground plane radio antennas
• Leslie S3 air horn