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Winter Blend vs Summer Blend Diesel

Did you know that diesel fuel has seasonal requirements that differ for both summer and winter? Read our guide to learn more

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Diesel Winter Blend vs Summer Blend – An Easy Guide

Did you know that diesel fuel has seasonal requirements that differ for both summer and winter?

How does diesel differ seasonally?

There are two grades of diesel, known as winter grade diesel and summer grade diesel and it’s worth knowing the difference between the two.

Winter grade diesel is formulated to contain an additive that prevents wax crystals forming at low temperatures, which means it will resist gelling in extremely cold temperatures. Winter fuel can be used all year round as it’s more resistant to cold (-12°C CFPP min) so it can be used in all seasons.

Summer grade diesel is optimised for summer use due to its slightly higher viscosity.

When is winter fuel available?

The blending of diesel is changed during the winter months to improve the cold-weather performance of the fuel. It’s available from 15 November to 15 March.

Summer fuel is available during the other period, and should only be used during these months.

Fuel certified for use during the summer period (summer grade diesel) is only fit for use during these months (-4°C CFPP min) as it has a limited resistance to the cold.

Summer fuel can only be used during summer

Fuel certified for use during the summer period (#2 diesel) is only fit for use during these months (-4°C CFPP min) as it has a limited resistance to the cold.

You could use winter-grade all year round, but it isn’t cost-effective. When refining crude oil, you get much less winter-grade diesel than summer grade diesel, which would result in problems with the availability of the winter grade. What’s more, the energy content of fossil winter-grade diesel is lower than that of summer grades.

Gas Oil Grade

What potential issues might occur when using the incorrect grade of diesel in winter or during cold periods?

Operational problems

The cold and wet winter months see some diesel-powered engines experience operative problems, such as difficulty starting and stopping the machinery, and vehicle and equipment failure.

If oil storage tanks or fuel systems have been designed poorly, there’s insufficient thermal protection or summer grade has been left in the tank during winter, wax crystals and condensation can form in the fuel which blocks filters and pipes.

Moreover, diesel fuel is refined so that its low-temperature properties fit the area and period to be used. But when seasonal cold snaps of weather emerge and the temperature drops below the cloud point of the fuel, functional difficulties occur due to wax drop out.

What is the cloud point?

The cloud point reports the temperature at which wax begins to crystallise and become noticeable to the eye. So in simple terms, it’s the lowest temperature at which fuel can be stored. A sample is cooled in a test jar and at intervals of 1°C to see if a haze ring forms at the bottom of the test jar.

Because summer grade fuel has a higher cloud point, it’s not appropriate to use during winter when a lower cloud point diesel is required.

Fuel contamination

Diesel Paraffins

Although wind does not lower the temperature level itself, it accelerates heat loss and causes more rapid cooling of the fuel contained in an unprotected or exposed storage tank. Water in the fuel and filters and the age and condition of the filters also cause clogging.

Ensuring your fuel is protected from bad weather conditions is imperative to avoid fuel contamination. Read on to learn what steps you can take to prevent fuel contamination, and also take a look at our diesel bug contamination guide.

Here at Crown Oil, we have a wide range of environmental fuel services on offer, such as fuel polishing, fuel testing, tank cleaning, fuel uplifting and fuel technical advice and guidance, to help keep your fuel in pristine condition.


All diesel fuel contains wax paraffins which are a noteworthy component that give it the high cetane number to enable efficient combustion. Ideally, these paraffins are a liquid and are dissolved in the diesel, but when diesel gets cold enough, the molecules begin to form crystals and solidify.

If the temperature drops enough, the crystals amalgamate and form large flat crystals which block the fuel filter. In some instances, the narrow bore pipework can bend which can cause unions to become completely blocked. This will cause the engine to fail or stop due to fuel starvation.

The same issues will transpire if the incorrect grade of diesel is used.
What are the tell-tale signs of paraffin problems?

  • A milky appearance of the diesel
  • A reddish deposit at the bottom of the tank
  • A reddish deposit on the surface of the fuel filter
  • Engines will be difficult to start or not start at all

What are the cold properties of diesel?

The cold flow specification is portrayed by the cold filter plugging point (CFPP) with a specification -12°C max in the winter and -4°C max in summer (British Standard BS2869).

CFPP is measured in a lab using the EN 116 standard. The method uses a progressively cool-down procedure, specific pumping conditions and a filter mesh size of 45 microns. It is developed by vehicle manufacturers in conjunction with oil companies and is used to exemplify the resistance to cold for all current European gas oils.

The CFPP test reveals a reliable correlation with engine performance and is used across Europe for all grades of diesel and red diesel to pinpoint the cold flow property of the fuel and as the specification parameter.

B2 2869, Section 8.2 – Seasonal Requirements

Gas Oil

Gas oil shall have the following maximum cold filter plugging point (CFPP) temperature in the given seasons. 

For A2 and D fuels distributed from refineries and imported into the United Kingdom:

  • Summer: 16 March to 15 October inclusive, -4°C
  • Winter: 16 October to 15 March inclusive, -12°C

NOTE 1: The term “distribute” is as defined in the Motor Fuels (Composition and Content) Regulations 1999 (10)

For Class A2 and D fuels for delivery from terminals:

  • Summer: 16 March to 31 October inclusive, -4°C
  • Winter: 01 November to 15 March inclusive, -12°C

For class A2 and D fuels for delivery to end users, the seasonality dates are given in Table 1, Part 1 and Part 2 of this British Standard, i.e.:

  • Summer: 16 March to 15 November inclusive, -4°C
  • Winter: 16 November to 15 March inclusive, -12°C

How can you protect your fuel against cold weather operating issues?

Manage your fuel

Summer quality fuels must not be kept in engines as winter embarks. If you have any leftover summer grade fuel and you fill your tank with winter fuel on top, you may deteriorate the cold weather characteristics of the winter grade diesel and likely experience undesirable machinery or equipment failure.

Make sure the entire volume of the tank meets the winter spec ahead of the winter period. To avoid winter waxing problems, we suggest you plan ahead and change over from summer to winter fuel by at least June. If you have any concerns regarding your diesel storage, our team of experts are happy to help, so call us today on 0330 123 1444.

Red Diesel Seasonal Grade

Shelter fuel tanks and engines

One of the most effective measures you can take to reduce paraffin crystal formation is to ensure your fuel is safe from contamination via safe storage of your fuel. Fuel containers and engines left exposed at night will cool quickly, so storage in a shed or undercover is strongly recommended to help avoid heat loss and paraffin problems.

Likewise, changing the fuel filter will help as a blocked filter will be less tolerant to small amounts of wax crystals.

Insulate tanks, filters and facilities

Another measure to take is to ensure effective insulation of tanks, filters and facilities. This is a cost-effective way to reduce waxing and expensive downtime.
Storage recommendations:

  • Clean the tank vent pipe to enable it to breathe
  • Remove any water in the fuel from condensation in tanks as this can freeze from 0°C and cause clogging of filters and pipes
  • Protect equipment from wind as it cools faster if unsheltered
  • Get your fuel tested regularly – paraffin crystals can settle, agglomerate and accumulate in the bottom of the tank and stop diesel from being pumped
  • Only require one delivery per year? Replenish your stocks during the winter season as this grade fuel can be used all year round
  • A minimum storage and handling temperature between 0°C and 5°C is recommended where extreme cold is expected
  • Insulate above ground storage and handling equipment
  • Insulate exposed tanks, pipes and pumps

Winter-appropriate lubricants

Lubricants and oils are important for cold weather operation. If the wrong oil is used, the engine will be less protected from friction and corrosion which can cause start-up problems.

If an engine oil experiences dilution by the fuel, sufficient wax may build up in the lubricating oil and cause it to solidify in cold weather.

Be sure to check the oil is liquid on the dipstick before starting. If you’re unsure, always change the oil prior to travelling into severe cold weather conditions.

Consider switching to HVO fuel

HVO fuel (hydrotreated vegetable oil) is a drop-in diesel replacement that is mobile and filterable to -32°C, so it will resist gelling in the worst of conditions, allowing your machinery to continue running all winter. Added to this, HVO is made from organic materials so it offers a 90% reduction in greenhouse gases and lower emissions. HVO is also FAME free, so diesel contamination is not an issue.


The use of additives can help improve the cold resistance of diesel, but please note, they must be supplied by an official supplier. If you use the incorrect additive, it can have an adverse effect and cause complications such as haze and water suspension.

How do additives work?

Cold additives (Middle Distillate Flow Improvers) don’t dissolve paraffin crystals that have already formed in the diesel. They work by modifying the crystal structure to ensure they decrease in size and don’t build up and form larger crystals which block the filters.

Additional additives must only be added when the fuel temperature is higher than the crystal formation temperature (cloud point) otherwise they will not be able to alter the crystal structure.

The problem is, however, that during the production of diesel, additives are already used to improve cold properties but in an extremely controlled environment at elevated temperatures. This makes it tricky to gauge whether cold flow properties can be improved or not.

The additive must be fully mixed to guarantee a regulated blend and any secondary treatment must be pre-diluted and free-flowing.

Case by case

Each case must be evaluated individually because the existing additive may have exhausted the sensitivity and response of the fuel to further additive treatment.

For fuel that does not contain any cold flow additive, the cloud point and CFFP results will be very alike. The cloud point for fuel that contains additives tends to be around 10°C above the CFPP level, which is why a waxy appearance might transpire when fuels are below the cloud point.

What is Crown Oil doing to minimise winter diesel problems?

Crown Oil supplies diesel that is suited for the season by varying the cloud point depending on the season and location.

Purchasing your diesel from the most trusted supplier in the UK gives you peace of mind that you are guaranteed a product that will never let you down. With nationwide coverage and quantities available in 205-litre barrels right up to 36,000 litres and more, we provide same day and next day deliveries for when you need us the most.

Crown HVO fuel boasts year-round performance. It has a high cetane number of up to 90 and a low cloud point  of-32OC, providing improved start performance, clean combustion and reduced chance of waxing than diesel in extreme temperatures. HVO meets EN 15940 standards and Fuel Quality Directive 2009/30/EC Annex II, so there’s no need to modify existing infrastructure. You can simply top up and go.

Discover more about Crown HVO fuel in our HVO fuel FAQ.

If you have any queries regarding the correct grade of diesel this winter, get in touch with us on 0330 123 1444 today to avoid encountering any operational problems this winter.

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