Cold flow properties of diesel

Diesel contains paraffin waxes that stay dissolved at ordinary temperatures. As the fuel cools, those waxes begin to crystallise — the point at which this becomes visible is the cloud point — and as cooling continues the crystals grow large enough to block fuel filters, at what is called the cold filter plugging point. Below the pour point the fuel stops flowing altogether. In a tank parked overnight in Eastern Ladakh, this is not a theoretical problem: the engine will not start, the fuel lines are blocked, and a vehicle that cannot move is a vehicle that is not available. Extreme weather grade fuels solve this by altering the composition and adding flow improvers that keep wax crystals small, so the fuel continues to pass through filters at temperatures far below the point at which ordinary diesel would have gelled.