Why do Train Engines/Locomotives Idle

If you ever passed a train station, or you are an avid railfan talking pictures of locomotives in a railyard, you must’ve noticed that every single locomotive you have encountered is either in motion or stopped, but idling.

Why do trains engines/ locomotives idle?

What is idling?

According to Wikipedia, idling refers to running a vehicle’s engine when the vehicle is not in motion, as an example, if you switch your car in P or N and you leave the engine on, your car is idling, which by the way can be illegal in some parts of the country/world.

Train engines/locomotives idle for several reasons.

If we can sort the reasons why a train idle in a chronological order (from starting to shutting down), we could start with the fact that turning on a locomotive is not as easy as turning on an auto vehicle.Many checks have to be done when starting a locomotive, which is time consuming, also fuel consumption is way higher at starting then when idling, engine also has to build up air pressure for certain checks, simply is easier, faster and cheaper to don’t shut off a locomotive unless is not going to be used for the next few good hours.
Another reason in a chronological order are mechanical inspections or repairs, that need the locomotive idling for checking certain aspects of the overall performance.
One aspect is well mentioning, the locomotives don’t use antifreeze for cooling the engine, but water. It is well known that if the temperature reaches close to 0 ℃ the water will freeze, this being catastrophic to any engine. For that reason, when it’s cold you’ll see locomotives idling more often.When the train crew changes, the train will be left idling as well.
Today’s locomotives in the United States are mainly diesel-electric, which means that a diesel engine drives an electric generator, the output of which provides power to the traction motors.These diesel engines are quite large, which translate in a way higher compression ratio than gas engines, repeated start-ups put these engines at risk of being damaged.
Modern locomotives might have a built in computerized system that automatically shuts off the engine under certain parameters, however they might still be idling for hours or even a day at a time.