With -20°C forecast in some parts of the UK, the Institute of Advanced Motorists (IAM) is warning drivers of diesel Land Rovers to remember that their fuel can wax over in extremely low temperatures, which could damage the fuel filter and cause a breakdown. Neil Greig, IAM Head of Policy and Research, said: "Waxing is the formation of crystals in the diesel which block the filter. If you drive a diesel vehicle, it pays to try and park in a garage or sheltered area, and try to not to leave your vehicle standing unused for too long. If you can’t park in a garage, do ensure that the engine bay of the car is parked downwind, so that the wind hits the back of the vehicle first. After starting the engine, let it idle for 10 minutes before driving off, as this will let the heat from the engine warm the filter and pipes."? ?Land Rovers with exposed fuel tanks and fuel pipes are most at risk but cars and vans can also be affected if it’s cold enough. Water in diesel fuel tanks and filters can also freeze. Mr Greig advised: "Keep the fuel tank full and, if possible, fill it before arriving at home as this will prevent the build up of condensation on the inside walls of the tank, helping prevent water building up in the bottom of the tank."? ? It's worth noting that oil companies supply winter diesel fuel that can withstand temperatures down to -15°C from October to March. and filling 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.