Starting a locomotive in cold weather is extremely hard and your chances or starting it are very slim to none. Starting them in good weather is often a 50/50 chance they will start depending on the age.
Generally speaking if the locomotive was running the day before you shouldn't have too much trouble starting it. If you frequently shut down the locomotive and start it you should have a pretty good feel how long to crank it and when to stop cranking.
The newer locomotives and the locomotives you start by pushing the red button in the cab are far more advanced then the older ones and usually start right up even in colder weather.
Most railroads even short lines will keep their locomotives running all the time when the temperature starts to get towards freezing. Cranking a locomotive in freezing weather will run the batteries down in less than 10 minutes if you can't get it to start.
Starting a locomotive is a science. It is important to get it right the first time it starts to turn over and keep it going. If we had a locomotive that was hard to start we would spray 4 cans of starting fluid in the airbox. That usually started it right up no matter how cold it was.
