Well the 071's have 126.8 litre engines (this one http://en.wikipedia.org/wiki/EMD_645) that produce 2,250 horsepower.
The Fuel Tanks are 3,600 L on each Loco.
As a rule of thumb, a large diesel will burn 3.5-4l of fuel per 20hp. So 2250hp/20=112.5 x 3.5l = 393.75 litres of fuel per hour at full tilt.
However, fuel consumed is proportional to the cube of the engine revs, so if the engine is at 65% power say, then power developed 65% x 65% x65% = 27% max = 607.5hp = 106 litres per hour.
On that basis, at an average 65% revs, the tank will last about 33 hours.