When the ambient temperature drops, the fluidity of diesel fuel decreases due to the concentration of paraffin. Diesel fuel becomes viscous like honey. For this reason, diesel fuel manufacturers add additives to winter fuel that increase fuel fluidity and ensure reliable engine start up to temperatures of minus 15°C (some varieties - up to minus 22°С).
However, these additives are not always available for reliable engine operation in winter. For this reason, the fuel filter is equipped with an electric heater. This prevents thickening of diesel fuel even in severe frost.