Munich - Winterised diesel is now on sale at the pumps of fuel stations. Its special additives protect the fuel from increasing in viscosity during cold weather and preventing it from being pumped to the engine. Car drivers once mixed petrol with diesel to improve fuel flow in sub-zero temperatures – but this may cause major damage to today’s engines, warn the experts at TÜV SÜD. They offer some tips about driving with diesel in
the winter months.
Now and again the old chestnut comes up that a little petrol should be mixed with diesel fuel in winter. Intended as good advice for diesel vehicle drivers, the tip of adding petrol to their diesel is not only long superseded but can actually cause damage to modern engines. TÜV SÜD expert Eberhard Lang has this warning: “Today’s winter diesel is already adequately protected against the process known as ‘waxing’ or ‘gelling’. Modern engines and fuel injection systems react poorly to petrol admixtures, and may even be damaged by the action if the worst comes to the worst.” The reason for this is that petrol reduces the lubricating abilities of the diesel oil, causing modern high-pressure pumps and fuel injection valves to suffer. As a consequence engine parts may suffer increased wear or possibly seize up, potentially resulting in complete failure of components or even the whole engine.
Cause:The diesel fuel sold in the summer months tends to undergo a process known as ‘waxing’ when temperatures drop slightly below zero; the paraffins in the diesel oil solidify into flakes of substances related to candle wax that can clog filters, lines, pumps and jets. As a result the engine fails to start, or stops going while drivers are on the road in low temperatures. The effect disappears when the car is brought into an environment such as a warm garage; however, the electronic systems in modern engines register the problem and may prevent the car from being restarted until they are reset.
What to do: For the past several decades, from November to the spring Germany’s mineral oil industry has only supplied fuel stations with ‘winterised’ diesels containing anti-waxing additives, which are guaranteed for use up to minus 20 degrees Celsius. Branded fuels in Germany generally offer protection against temperatures of up to minus 22 - minus 28 degrees Celsius. Austria and Switzerland likewise supply winterised diesel; in fact, Swiss fuel stations even stock ‘polar diesel’ in chillier regions. This is a fuel type also widespread in Scandinavia that is safe up to a minimum of minus 30 degrees. However, fuel stations do not provide winterised diesel in more southern climes where frost is a rarity. For drivers that fill up their tanks in Southern Italy, planning to make the most of the high mileage of their low-cost diesel by travelling to the Alps, Lang advises refuelling before they hit the colder areas.
Reserve: The TÜV SÜD expert also points out a further source of risk: depending on when and where the reserve fuel can was last filled up, it may contain summer diesel. “If summer diesel is used to refuel a vehicle in an emergency, we urgently advise filling up at the next fuel station. This will dilute the summer fuel with fuel that can cope with the ambient temperatures”, says Lang. Of course, filling the reserve can with winterised fuel is the safest procedure of all.
Water: If a diesel vehicle fails to start in cold weather, the culprit could be a further property of this fuel type: its water content. Diesel oil always contains a small quantity of water, which is usually extracted and collected by a special filter in the engine. However, it may also freeze in the engine and block the fuel supply system. Regular filter maintenance by professionals is helpful to prevent this. While many modern cars have a filter heating system, this will be of no avail if the car has been parked in the bitter cold.