* Thickened Fuel: Diesel fuel, unlike gasoline, has a higher viscosity (thickness). In cold weather, this viscosity increases dramatically, making it difficult for the fuel pump to draw it into the fuel system. This is exacerbated by the presence of paraffin wax in the fuel; as temperatures drop, this wax can crystallize, clogging fuel filters and lines, effectively starving the engine of fuel. Fuel additives are designed to mitigate this problem.
* Difficult Ignition: Diesel engines rely on compression to ignite the fuel. Cold temperatures lower the air density inside the cylinders. This means less air is compressed, resulting in lower combustion temperatures. This makes it harder to reach the ignition temperature required for the diesel fuel to auto-ignite. The glow plugs (or glow coils in newer systems) assist with this, but if they're faulty or insufficient for the extreme cold, starting will be impossible.
* Battery Issues: Cold temperatures significantly reduce the effectiveness of a battery. A weakened battery may not provide enough cranking power to turn the engine over quickly enough to build sufficient compression for ignition, especially if the engine oil is also thick.
* Thickened Oil: Like the fuel, the engine oil becomes thicker in cold weather. This increases the resistance on the engine's moving parts, making it harder to crank the engine over. The thicker oil also slows down the engine's internal lubrication, leading to increased wear and tear if forced to start under these conditions.
* Water in Fuel: Water in the fuel will freeze at lower temperatures, leading to blockages in the fuel lines and filters. This can further exacerbate the problem of fuel delivery.
* Glow Plug Failure: As mentioned earlier, glow plugs are crucial for preheating the air in the combustion chamber to aid ignition. If a glow plug malfunctions or is not working efficiently, starting in cold weather becomes much more difficult or impossible.
In summary, cold weather creates a perfect storm of problems for a diesel engine, impacting fuel delivery, ignition, and the overall ability of the engine to turn over. Addressing these potential issues through preventative maintenance (e.g., using winterized fuel, ensuring battery health, checking glow plugs) is crucial for reliable cold-weather operation.
