Why are diesels left to idle so much instead of being shut down?
Most diesel locomotives use water as coolant. If the unit is left shutdown for an extended period of time in freezing temperatures, the water will freeze. This could damage the locomotive since water expands as it freezes. Most railroads have rules that locomotives cannot be shut down in temperatures below 40 degrees unless the water is drained. Since starting diesels is time consuming, they are frequently left running even in warmer weather. Fuel consumption drops to only a few gallons per hour in idle mode.
