Why Diesel Locomotives Never Turn Off

Added: 2026-05-23

[00:00:00]A diesel locomotive can burn 7 gallons of fuel every hour while sitting completely still in a railyard, >> [music] >> going nowhere.

[00:00:07]Across North America, that adds up to more than 20 million gallons of wasted diesel every year.

[00:00:13]But railroads aren't doing this out of laziness.

[00:00:16]So what is actually stopping them from turning these engines off?

[00:00:20]The answer involves frozen water, compressed air, federal safety regulations, and an industry that spent decades [music] choosing the lesser of two very expensive problems.

[00:00:33]The diesel engine inside a modern freight locomotive is not anything like the engine in your truck. It is closer in scale to the kind of engine you would find [music] bolted to the deck of a small cargo ship.

[00:00:43]The most common prime movers on North American railroads are EMD 645 and 710 series, massive two-stroke V16 diesels originally designed by General Motors Electro-Motive Division.

[00:00:57]Each cylinder in a 645 series engine displaces 645 cubic inches of volume.

[00:01:03]That is more than 10 L per cylinder.

[00:01:06]Multiply that by 16 cylinders, and the total displacement of one of these engines exceeds 10,000 cubic inches.

[00:01:12][music] For comparison, a large pickup truck engine might displace around 6 L total.

[00:01:19]The locomotive engine is roughly 28 times larger.

[00:01:22]These engines do not use spark plugs.

[00:01:24][music] They are compression-ignition diesels, meaning the fuel ignites when air inside the cylinder is compressed to such extreme pressure that it reaches ignition temperature on its own.

[00:01:36]In a warm operating engine, this works beautifully.

[00:01:39]The metal is at operating temperature, the lubricating oil flows freely, and the turbocharger is spinning at thousands of revolutions per minute.

[00:01:47]However, when one of these engines sits cold in a railyard overnight and the temperature drops below freezing, everything changes.

[00:01:56]The lubricating oil thickens into something closer to syrup. The massive pistons and connecting rods resist movement because the oil can no longer reduce friction effectively.

[00:02:07]The starter motor, powered by a bank of lead-acid batteries, has to overcome all of that resistance to crank the engine.

[00:02:14]>> [music] >> And those same batteries lose a significant portion of their output in cold weather, right when you need them most.

[00:02:20]Even if the starter manages to turn the engine over, the cold cylinder walls may not allow the compressed air to reach ignition temperature.

[00:02:28]The engine cranks and cranks, >> [music] >> but it refuses to fire.

[00:02:33]When a cold locomotive does finally start, the process is not [music] instant.

[00:02:38]Depending on conditions, it can take 10 to 20 minutes of careful warm-up before the engine is ready for service.

[00:02:45]The cooling system must reach operating temperature gradually to prevent thermal shock, which can crack cylinder liners and warp the engine block.

[00:02:54]During that entire warm-up period, the locomotive cannot be loaded to full throttle. A GE patent filing noted that in cold weather conditions, there may be a delay of more than 1 hour after starting before the engine is capable of operating at full power.

[00:03:09]For a railroad that needs a locomotive ready to move freight within minutes of a crew arriving, that kind of delay is not acceptable.

[00:03:17]But what if the cold start problem were the only issue? Could railroads not solve it with better batteries or block heaters and call it a day?

[00:03:24]They could try, but that is only the first reason these machines stay running.

[00:03:29]The second reason is something that surprises almost everyone who learns about it. And it involves water.

[00:03:36]Unlike the engine in your car, which circulates a mixture of water and ethylene glycol antifreeze, large North American railroad locomotives use plain water as their engine coolant.

[00:03:48]Not a water and antifreeze blend.

[00:03:50]The coolant is water, sometimes treated with corrosion inhibitors, but fundamentally nothing more than that.

[00:03:57]Why would any railroad do this?

[00:03:59]A locomotive cooling system holds anywhere from 200 to 600 gallons of coolant.

[00:04:05]Filling that volume with antifreeze would cost several thousand dollars per locomotive, and the expense repeats every time the system is serviced or flushed.

[00:04:14]Beyond cost, the engines themselves were not originally designed for glycol-based coolants.

[00:04:20]Railroad maintenance crews discovered over the decades that antifreeze mixtures caused problems with certain gasket materials and internal seals.

[00:04:29]One railroad attempted to switch its fleet [music] to a water-glycol cocktail, and the result was a maintenance nightmare.

[00:04:36]Microbes grew in the jacket water system.

[00:04:39]The glycol's lower heat transfer coefficient meant the engine ran hotter without producing more power.

[00:04:44]And standby circulator pump seals failed so frequently that a locomotive had to be pulled from service nearly every week.

[00:04:51]Water, by contrast, is cheap, transfers heat more efficiently, and poses no environmental hazard if a hose fails and the coolant spills onto the track bed.

[00:05:02]But the trade-off is obvious.

[00:05:04]Water freezes.

[00:05:05]>> [music] >> And when several hundred gallons of water freeze inside the intricate passages of a locomotive engine block, the expanding ice cracks cast iron, splits cooling passages, and destroys the prime mover.

[00:05:21]Replacing a cracked engine block is not a routine shop visit.

[00:05:25]It can take a locomotive out of service for weeks and cost hundreds of thousands of dollars.

[00:05:31]So, railroads adopted a simple operating rule for their locomotive fleets.

[00:05:35]When ambient temperatures drop below about 35° F, 2° C, the engines stay running.

[00:05:44]In extreme cold, in places like northern Minnesota, Montana, and the Canadian prairies, where winter temperatures regularly fall to minus 20° F or minus 30° F, locomotives are not idling at their lowest setting.

[00:05:59]Crews set them to run at notch three or four, burning even more fuel because the engine at idle cannot generate enough heat to keep itself warm against that kind of cold.

[00:06:09]The alternative is draining the entire cooling system, which is time-consuming and creates its own cascade of problems when the locomotive needs to be refilled and returned to service.

[00:06:20]How do you dispatch a drained locomotive on short notice when a crew is waiting and freight is falling behind schedule?

[00:06:27]In practice, you do not. You keep it running.

[00:06:31]Now, there is a third reason locomotives stay running, and it might be the most critical one of all.

[00:06:37]This one has nothing to do with the engine or the coolant. The third reason is all about the brakes.

[00:06:43]Every freight train in North America uses an AIR brake system.

[00:06:48]The brakes on each car in a 100-car consist are powered by compressed air supplied through a continuous brake pipe that runs the full length of the train.

[00:06:58]The source of that compressed air is a compressor mounted on the locomotive driven directly by the diesel engine.

[00:07:05]While the engine runs, the compressor maintains pressure throughout the brake system.

[00:07:10]When the engine stops, the compressor stops, too.

[00:07:14]Here's the part that catches people off guard. Train brake systems leak constantly, and this is considered entirely normal and expected.

[00:07:23]Every coupling between cars, every hose connection, every valve and gasket in a 100-car train allows some small amount of air leakage.

[00:07:33]If you have ever stood on a station platform and heard that steady hissing sound from underneath a parked train, that is brake line air escaping.

[00:07:43]Federal Railroad Administration regulations set specific limits on acceptable leakage rates, but the leakage never reaches zero.

[00:07:51]As long as the locomotive engine is running and the compressor is cycling, this leakage is continuously replenished. The system stays pressurized and the brakes remain ready.

[00:08:01]However, if the engine is shut down and the compressor stops, the brake system begins losing pressure.

[00:08:08]After about 4 hours without air according to Federal Railroad Administration rules, the air test performed on that train is no longer valid. Before the train can move again, a crew must perform a new class one air brake test. For a long freight train, that means a conductor walking the entire length of the consist, inspecting each car, and confirming each brake cylinder responds correctly. On a 90-car train, that walk alone can take over an hour. The full test process can consume several hours and tie up a crew that could otherwise be running a train.

[00:08:41]Inspecting every car is time-consuming, and this is not a corner case. Trains sit in yards and on sidings constantly, waiting for crew changes, track clearance, or loading operations.

[00:08:55]Every time a locomotive engine shuts down with a train attached, that clock starts ticking toward a mandatory retest.

[00:09:03]For a railroad managing hundreds of trains per day across a network spanning the continent, those retests do not stay isolated. They ripple outward, delaying connections, backing up traffic at junctions, and pushing already tight schedules past their limits. If you are enjoying this look behind the scenes of how railroads actually operate, hit subscribe.

[00:09:27]We cover locomotive history and railroad engineering every week.

[00:09:31]Now, let's talk about the real calculation happening inside every railroad operations center.

[00:09:37]The of the diesel fuel burned while the locomotive idles is less than the cost of the labor, the operational delay, and the cascading schedule disruptions caused by a full air brake retest. But which cost is actually bigger?

[00:09:53]Railroads looked at both numbers decades ago, and the answer was not even close.

[00:09:58]They chose to keep the engines running.

[00:10:00]Those three factors, the cold start problem, the water coolant dilemma, and the air brake system explain why idling became standard practice from the very beginning of the diesel locomotive era.

[00:10:14]The decision was not born from carelessness or waste. Idling was a calculated choice, and for most of railroad history, it was the right one.

[00:10:23]But the costs kept climbing as fuel prices rose and environmental regulations tightened across the country.

[00:10:29]Communities near rail yards filed complaints about the constant noise and exhaust fumes from idling locomotives at all hours of the night.

[00:10:37]And the sheer scale of the waste became harder to ignore.

[00:10:40]The Environmental Protection Agency estimated that switching locomotives alone consumed 60 million gallons of diesel fuel per year while doing nothing but sitting still.

[00:10:51]So what changed?

[00:10:53]The industry started developing alternatives, and the first major technology was the automatic engine start-stop system, known as AESS.

[00:11:03]These systems monitor a locomotive's coolant temperature, oil temperature, air brake pressure, battery charge, and ambient conditions.

[00:11:12]When all parameters are within safe limits, the system shuts the main engine down. If any reading drifts outside its threshold, the engine restarts automatically. [music] Canadian Pacific was among the first railroads to install them aggressively, rolling out a system called [music] SmartStart across large portions of its fleet.

[00:11:31]Early versions were timer-based.

[00:11:33]Modern versions use microprocessor controls that can track dozens of variables simultaneously >> [music] >> and make restart decisions in seconds.

[00:11:42]AESS works well in moderate weather when locomotives sit in temperate rail yards.

[00:11:48]In spring and fall, the system can cut unnecessary engine idling time in half.

[00:11:53]But does it solve the problem in January in Saskatchewan?

[00:11:56]Not entirely.

[00:11:58]When coolant temperatures drop quickly in sub-zero air, the system restarts the engine so frequently that the fuel savings shrink.

[00:12:06]And in extreme cold, below minus 10° Fahrenheit or below minus 15° Fahrenheit, many AESS systems are programmed not to shut the engine down at all because the risk of a failed restart is too high.

[00:12:22]That limitation led to the development of the auxiliary power unit or APU.

[00:12:28]An APU is a small, separate diesel engine, typically around 25 horsepower, installed in the locomotive nose compartment.

[00:12:37]When the main engine shuts down, the APU takes over.

[00:12:41]It drives a small generator to keep the batteries charged and the electrical systems powered.

[00:12:46]The APU also circulates heated coolant through the main engine block to prevent freezing.

[00:12:51]And it runs a small compressor to maintain brake line pressure.

[00:12:55]All of this at a fraction of the fuel consumption.

[00:12:58]A locomotive APU burns roughly 3 L of diesel per hour compared to the 25 L or more that the main engine consumes at idle.

[00:13:07]The savings are real.

[00:13:09]Indian Railways reported projected annual savings of over 60 crore rupees after fitting auxiliary power units to their diesel fleet.

[00:13:18]North American railroads have documented annual fuel savings in the range of several thousand gallons per locomotive.

[00:13:24]A New York state study found that diesel-fired warming systems could [music] achieve payback in as few as one to three winter seasons.

[00:13:32]But if the technology works, why has not every locomotive been converted?

[00:13:37]The answer is partly mechanical >> [music] >> and partly human.

[00:13:41]Auxiliary power units add another diesel engine to maintain with its own oil changes, belt replacements, and reliability concerns.

[00:13:50]Maintenance departments already stretched thin are not always eager to service auxiliary systems that are not considered mission critical.

[00:13:58]And then there is the human factor.

[00:14:00]Locomotive engineers who have spent their entire careers knowing that you never shut down a diesel have a deep, trained reluctance to trust an automated system.

[00:14:10]If the APU fails overnight and the main engine cools to dangerous temperatures, the engineer arriving at 5:00 in the morning faces a locomotive that will not start and a train that cannot move.

[00:14:22]More than one crew has quietly disabled the automatic engine start-stop system or the APU to eliminate that risk, accepting the fuel waste as the price of certainty.

[00:14:33]Can you blame them?

[00:14:35]When your job depends on a locomotive being ready to move at the moment a dispatcher calls, the consequences of a failed restart are not abstract. They are a missed freight window, a congested mainline, and a supervisor asking why the train did not leave on time.

[00:14:50]The old way, keeping the locomotive idling, never produced that phone call.

[00:14:55]The tension between tradition and efficiency is real, and it plays out in rail yards across the continent every night.

[00:15:03]But the economics are shifting in ways that even the most cautious engineers can't ignore.

[00:15:08]Diesel fuel isn't getting cheaper.

[00:15:10]Railroad profit margins are under constant scrutiny from shareholders, and environmental regulations carry real penalties now.

[00:15:18]The EPA emission standards for locomotives have tightened through multiple tiers, and idle reduction isn't optional for railroads that want to meet their sustainability commitments.

[00:15:28]Looking forward, the landscape is shifting in ways that go beyond idle reduction gadgets.

[00:15:33]Battery-electric locomotive prototypes are entering trial service on short-line railroads and in yard switching operations, where the duty cycle of frequent starts and stops makes electrification most practical.

[00:15:45]Hydrogen fuel cell locomotives are in early research stages for longer hauls where battery weight becomes prohibitive.

[00:15:52]Energy management systems, like Wabtec's Trip Optimizer and New York Air Brakes Leader system, are optimizing not only how locomotives haul freight, but how they manage energy while sitting still.

[00:16:04]Some railroads are also experimenting with shore power connections in yards, plugging locomotives into external electrical sources, the way you would plug in a block heater on a truck in Manitoba, keeping the engine warm and the systems charged without burning a drop of diesel.

[00:16:19]The diesel locomotive won't disappear overnight.

[00:16:22]There are thousands of them in active service across North America, and they're built to last 40 years or more.

[00:16:30]Many of the EMD 645-powered SD42 locomotives that entered service in the 1970s are still hauling freight today.

[00:16:39]Their engines rebuilt and their frames showing no sign of retirement.

[00:16:44]The 645 and 710 prime movers remain among the most durable and maintainable large diesel engines ever mass-produced, and they'll be rumbling through rail corridors for years to come.

[00:16:57]But the practice of letting them idle indefinitely is slowly fading.

[00:17:02]Not because anyone suddenly realized it was wasteful. The railroads always knew that.

[00:17:07]It's fading because the alternatives, from auxiliary power unit engines to shore power hookups in modern rail yards, are finally reliable enough and affordable enough to change the math.

[00:17:19]The next time you drive past a railyard at night and hear those engines rumbling in the dark, you'll know what's actually happening.

[00:17:26]It isn't carelessness. It's a compromise between physics, economics, and the relentless demands of keeping freight moving across a continent. A compromise that took decades to build and one that is only now beginning to change.