 A disadvantage of diesel as a vehicle fuel in cold climates is that its viscosity increases as the temperature decreases, changing it into a gel (see Compression Ignition – Gelling) that cannot flow in fuel systems.Special low-temperature diesel contains additives to keep it liquid at lower temperatures, but starting a diesel engine in very cold weather may still pose considerable difficulties.Another disadvantage of diesel engines compared to petrol/gasoline engines is the possibility of diesel engine runaway failure.