Unlike truck or automobile engines, locomotive engines cannot use antifreeze in their cooling systems for technical reasons related to reactions of antifreeze chemicals on internal engine parts. Therefore, during cold weather, a locomotive engine must either be working to transport freight or idling to prevent freezing. A freeze-damaged locomotive engine can cost upwards of $200,000 to repair.
Recognizing the need to continuously reduce fuel consumption and exhaust emissions, the railroad industry and its suppliers developed the Auxiliary Power Unit, or APU, which is a small diesel engine that automatically operates via computer control whenever the main locomotive engine is shut down and ambient temperatures are close to or below freezing. Heat from the small engine is transferred to the larger engine via fluid transfer connections to prevent freezing. The APU keeps the main engine warm, reducing fuel consumption and emissions while the main engine is shut down.
While a typical locomotive main engine burns five gallons of diesel fuel per hour while idling, the APU consumes only one gallon. When G&W monitored data for a 15-month period from one of its Canada Region locomotives equipped with an APU, fuel savings averaged more than 20 gallons per day. Over a typical year, the APU can reduce emissions from one locomotive by more than 80 tons of nitrogen oxides, 12 tons of carbon monoxide and three tons of particulate matter.
G&W has installed more than 200 APUs on its locomotives in order to reduce fuel consumption in its colder operating regions.