Traditionally, the cold operability of diesel vehicles has in very low temperatures been guaranteed by high-quality special fuels. This means increasing costs and decreasing yields from crude oil for an oil refiner. With the increase in use of diesel fuel, its properties are altered. The most significant alteration is the increase of specific gravity and viscosity. The use of de-waxing processes and flow improvers is also increased.Cold tests were carried out on six diesel-powered vehicles using Finnish diesel fuels. The cold operability of a conventional fuel system is within the CFPP range. In a well-designed system, the lower operability limit is some 6°C below the CFPP. Using extra equipment to warm the fuel, it is possible to lower the cold operability limit 10…15°C below the CFPP. In this case, the limit is reached because of fuel pumpability.