Winter Diesel Problems

All diesel fuels contain wax which is considered an important diesel component because of its high cetane value. Normally the wax is a liquid in the fuel; however, when diesel fuel becomes cold the wax starts to crystallise. This problem is known as waxing, a process where wax crystals in the fuel freeze over, causing a blockage in fuel lines and filters and, in some cases, damaging the fuel filter. This means the engine could be hard to start or not start at all.

The problem is more often found in extreme cold, and tends to affect larger commercial vehicles more than cars or vans because of the more exposed engines. Most diesel suppliers add additives to diesel to reduce the risk of waxing however; if you do have a problem with your engine starting, you can check if the problem is waxing in the following way:

  1. Check engine oil
  • Check your dipstick to see if the engine oil is fluid. Waxing diesel could have occurred in the crankcase. If this is the case do not start the engine.
  1. Check the fuel filter
  • If the engine fails to start after an oil change, the fuel filter could be blocked with frozen wax. It will be visible as a white or yellow residue in the fuel.


How can I prevent waxing?

The simplest way of preventing waxing is to park your vehicle somewhere warm e.g. a garage or indoor car park. However, as this is not always possible, there are some other things that may help you avoid waxing in extremely low temperatures.

  1. Park the vehicle so that the engine bay is downwind, so that the rear takes the brunt of the cold wind.
  2. Always warm the engine by letting it idle for ten minutes before driving the vehicle. This allows the filter and pipes to warm up before setting off.
  3. Always check the water in diesel fuel tanks and filters in fluid.
  4. Never leave the vehicle standing unused for too long.
  5. Keep the fuel tank as full as possible to reduce the possibility of condensation on the walls of the tank.
  6. Many petrol stations will provide diesel which is appropriate for winter driving. Petrol stations sell fuel protected down to -15°C in winter. Additives are available but they should be mixed with the fuel before it gets cold, not after. They may also affect the warranty on the engine.

Your local Ford dealership can advise you on adding special additives to your fuel to prevent waxing. We would recommend you do not attempt this yourself as your local Ford dealership will know the exact type of additive and how much to put in so that your engine isn’t damaged.


Additional Information

Auxiliary Heaters

Fuel Contamination and Water in Fuel


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