BB00.40-P-0137-00A Winter Operation With Diesel Fuels
BB00.40-P-0137-00A Winter Operation With Diesel Fuels
1. General
At low outside temperatures, the viscosity of the diesel fuel can be negatively influenced due to precipitation of paraffin crystals. This can lead to delivery problems resulting from the filter and/or fuel lines clogging up. To prevent such problems, winter diesel fuels with improved cold viscosity characteristics are available on the market during the winter months. In most cases, these are suitable for the outdoor temperatures usually occurring.
In Mercedes-Benz vehicles, measures have been taken that lead to quick heating of the fuel. With unsuitable fuel grades in combination with very low temperatures, however, filter clogging may occur.
1.1 Diesel fuel with improved cold viscosity properties
We recommend only using winter diesel fuels for which a cold resistance of at least -20 °C and lower is guaranteed by the fuel supplier.
In Europe, various climate-dependent Arctic Grades are defined in the standard EN 590. The utilization times and the Arctic Grades to be used are regulated individually for every country on the national level. The following requirements are valid for Germany and are also defined in the new DIN 51628:
To ensure the operational safety of the vehicle, the season-dependent fuel grade is to be taken into account when fueling the vehicle.
2. Remedies when fuel is not sufficiently resistant to low temperature
2.1 Admixture of kerosene, aviation turbine fuel, gasoline in diesel fuel
For all Mercedes-Benz passenger cars and commercial vehicles, the addition of kerosene or aviation turbine fuel to improve the cold resistance is no longer permissible due to possible negative effects on the injection system due to insufficient lubricity.
The use of gasoline is not permissible because it impairs the fuel's lubricity and for reasons of safety (flash point reduction).
2.2 Flow improvers for diesel fuels
2.2.1 General
Although flow improvers cannot prevent paraffin from precipitating out, they do have a great deal of influence on the shape and growth of the crystals. As the fuel cools off, a large number of modified paraffin crystals forms that can pass through the fuel filter. The fuel can still flow and be filtered, because formation of unsuitable crystals is prevented. By adding flow improvers, a winter diesel fuel can be made from a summer or intermediate diesel fuel or winter fuels can be improved in terms of their low-temperature performance.
It should be noted here that the effectiveness of these additives depends on the origin of the base fuel as well as the refining process and addition of flow improvers at the refinery. Reliable information can therefore be provided only by laboratory testing of the cold filter plugging point or an extensive bench test in a climatic chamber during which the low-temperature performance is checked.
2.2.2 Use
The correct metering and good mixing of flow improvers are crucial in order to achieve an improvement in the cold resistance. Flow improvers only exhibit a good response time up to a certain mixing ratio. Overdosage can possibly even lower the cold resistance and must therefore be avoided. Only those flow improvers tested and approved by Mercedes-Benz are to be used. All flow improvers approved by Mercedes-Benz are listed in sheet no. 137.1. Sheet no. 137.1. The recommendations made by the manufacturers of the flow improvers approved by Mercedes-Benz must be complied with exactly.
Upon adding the additive, the temperature of the winter diesel should be at least 5 °C and the summer diesel at least 8 °C. Adding shortly after the paraffin has already precipitated out has no effect. In this case, the only remedy is to heat up the entire fuel system. If flow improver is added to the diesel fuel in the vehicle tank, the vehicle should be refilled immediately to mix the flow improver and the engine should then be operated until the mixed fuel is present in the entire fuel system. Failure to observe this can result in the unmixed fuel in the lines and fuel filter causing malfunctions.