When winter comes knocking, there’s no better way to answer than with guaranteed protection of your diesel during the cold winter months. Did you know that diesel differs in specification?

What does this mean?

It means that winter diesel can be used all year round as it’s more resistant to the cold, but summer fuel is only certified for use during summer because it has a limited resistance to the cold.

You could use winter fuel all year round, however this is not cost-effective. When refining crude oil, you get less winter grade than summer grade diesel meaning there may be not enough winter grade available. The energy content of fossil winter grade fuel is less than summer grade.

Winter fuel has a specification of a cold filter plugging point (CFPP) of -12°C max, whereas summer fuel has a -4°C max in summer (British Standard BS2869). This can cause big problems.

Why is this?

If you use summer grade diesel in winter or you leave some left over in the bottom of your fuel tank, engines can have difficulty starting and machinery and equipment can fail.

This is because wax crystals and condensation form in the fuel which block filters and pipes.

Winter diesel is refined so that its low properties suit the area and period to be used. However, in periods of severe cold weather, the same issues such as performance problems can occur. The temperature drops below the cloud point, causing functional difficulties due to wax drop out.

The cloud point reports to the temperature where wax begins to crystallise which can be noticed by eye. It’s basically the lowest temperature at which a fuel can be stored. Since summer grade fuel has a higher cloud point, it’s not suitable to be used in winter as a lower cloud point of diesel is needed.


Diesel contains wax paraffins which are an important element that give the fuel the high cetane number to permit efficient combustion. These paraffins are ideally in liquid form so they can be dissolved in the diesel, but when it becomes too cold, the paraffins start to form crystals and solidify.

When the temperature drops significantly, they will amalgamate and create large flat crystals that block the fuel filter. This will cause the engine to fail because the fuel is starved. The same happens when summer fuel is used in winter.

How to tell when diesel contains wax paraffins/crystals

Yes, the fuel will have different properties that can be seen by eye:

  • A red-tinged deposit on the bottom of the fuel tank
  • A red-tinged deposit on the surface of the fuel filter
  • A milky appearance in the fuel
  • Difficulty starting engines/not starting at all

If you suspect wax paraffins in your fuel, give us a call today on 0330 123 3773 and we’ll be able to provide expert advice and offer a first-class solution.

What precautions can you take?

  • Buy your diesel ahead of the winter
  • Ensure no leftover summer grade fuel is left in your tank – it can deteriorate the cold weather characteristics of winter fuel
  • Store your fuel tank in a shed or garage to protect from the cold weather and wind
  • Get your fuel tested regularly – wax crystals can settle and build up at the bottom of your tank which can stop diesel being pumped out the tank
  • Use winter appropriate lubricants to avoid wax build-up from the wrong oil type used
  • Use additives provided by an official supplier
  • Purchase your diesel from Speedy Fuels

How do additives prevent paraffins?

Cold additives, also known as Middle Distillate Flow Improvers work by modifying the crystal structure to enable them to reduce in size and ensure they don’t amalgamate and form larger crystals to block the filters. They don’t dissolve crystals already formed.

Additives must only be added to the diesel when its temperature is higher than the cloud point as they cannot alter the crystal structure. The issue is that during the production of diesel, additives are used already to improve cold properties but in a highly controlled environment at elevated temperatures. This means it’s difficult to determine whether cold flow properties can be enhanced or not.

Each case must be looked at singularly as the existing additive could have already exhausted the sensitivity and response, meaning further treatment is not effective. Diesel fuel that does not contain any cold flow additive will have cloud point and CFFP results that are very similar. The cloud point for fuel that contains additives tends to be around 10°C above the CFPP level, which is why the fuel may have a waxy appearance when fuels are below the cloud point.

How do you buy winter grade diesel?

The blending of diesel is automatically changed during the cold months in order to improve cold weather performance of the fuel. It’s available from 15th November until 15th March to ensure everyone gets the most out of their equipment, vehicles and machinery.

We automatically adjust the quality of our product at no extra cost to supply you with the correct fuel all year round. From 205-litre barrels right up to 36,000 litres and more, we can get your delivery to you before you know it.

If you have any questions regarding the seasonal requirements or want to buy our high-quality diesel, call us today on 0330 123 3773 and we’ll be happy to help you