The gelling point of diesel fuel is the temperature at which the paraffin wax naturally present in the fuel begins to solidify, forming crystals. This crystal formation causes the fuel to thicken, eventually leading to a point where it cannot flow properly through fuel lines and filters. This phenomenon is a major concern in colder climates, as it can disable diesel engines. As an example, standard diesel fuel may start to cloud around 20F (-7C) and gel at a lower temperature, potentially rendering a vehicle inoperable.
The thickening of diesel fuel at low temperatures can have significant consequences. It can lead to fuel starvation, preventing the engine from starting or causing it to stall during operation. This can result in costly breakdowns, delays in transportation, and potentially dangerous situations. Historically, fuel suppliers have implemented various strategies, like adding additives and offering winter-grade fuels, to combat this problem and ensure reliable operation of diesel-powered equipment in cold weather conditions.