It tottaly depend on speed and how much load a diesel loco is carriying.I think that mileage of ALCO is 6l/km.EMDs are very feul efficient 3-4l/km.When a loco is hauling a heavy load it needs much power and acceleration that means its engine need more diesel consumption but its speed is slow.In this way the mileage of diesel loco becomes low.I think Alco covers 1500-2300km with full tank.