Which of the following strategies is a requirement for starting diesel engines in subzero (below −17°C) temperatures?

Using an auxiliary diesel coolant heater is essential for starting diesel engines in subzero temperatures because these heaters warm the engine coolant, which in turn helps to raise the temperature of the entire engine. Diesel engines rely on adequate compression and temperature for ignition, and when the temperature drops below freezing, oil thickens, and fuel injectors may not work efficiently. The coolant heater ensures that the engine block reaches a more favorable temperature for startup, thereby reducing the risk of starting failures and minimizing wear on engine components during cranking.

This approach is particularly important because it directly addresses the physical properties of diesel fuel, which can gel at low temperatures, making it harder to pump and atomize. By pre-heating the coolant, the auxiliary heater effectively mitigates these challenges, allowing for a smoother and more efficient start.

In contrast, while ether can sometimes be used as a starting aid in extreme conditions, its use carries risks such as potential engine damage or fire hazards. Additionally, avoiding shutting off the engine may help maintain operational readiness in frigid conditions, but it isn’t a practical or universally applicable strategy. Hence, relying on an auxiliary coolant heater is the most effective and widely accepted method for ensuring reliable diesel engine starts in severe cold conditions.