iced up 4x4
Technical Top Tips

Three Things to know about Diesel for Winter Motoring … but not often mentioned

For certain areas of Europe & the UK, it has been winter for a few weeks or even months now.

The usual advice is anti-freeze condition, a good battery and charging it, wiper blades, demisters, ice scrapers and the de-icer tin in the boot.

We thought this would be a good time to touch on a topic that most people don’t think about and that is fuel.

Fuel that you buy in the summer isn’t the same as the fuel you buy during the winter. Refineries have multiple blends they use depending on the time of the year. The main reason for all the difference in blends is the weather, or more to the point temperature.

Naturally, you would think that cold weather means more power. The air is denser, so there is more oxygen per volume of air. Unfortunately, while the colder air is great for oxygen content, it is really bad for diesel fuel.


1, The Hard Start

Diesel engines are compression ignition engines. The process of ignition happens when the fuel being injected into the engine mixes with hot air.

glow plug
Image; Beru

As the fuel is rapidly heated up by the air, it auto ignites. When the engine is cold and the air is cold, there may not be enough heat present to auto ignite the fuel. This is why manufacturers have installed grid heaters and glow plugs. These are designed to heat up the air enough to reach auto-ignition.

What can you do? Well, at night you can plug in your motor. By keeping the engine block warm, the air will heat up more during compression helping to achieve auto ignition. If you do not have this option, many later vehicles have their own pre-heaters installed for use upto an hour before you start your journey. These however are reliant on the vehicle battery. This is the time of year when people find out their batteries are bad and they are left out in the cold. Make sure your charging system is working well and your batteries are in good shape. The starter needs all the amperage it can handle to turn over the engine when it is cold and more power is needed to heat those glow plugs.


2, Filter Gelling


Depending on where you live and how long you have driven, will determine whether you have experienced fuel gelling or if you know about it.

image; powerstroke

Fuel gelling is a process at which the paraffin’s in diesel fuel begin to crystallize enough to prohibit fluid flow. If you do a quick search on the internet, you will find people giving many different temperature ranges which at this phenomenon happens (anywhere from 4 to -30 degrees Celsius). Why the wide scope you may ask?

The primary reason for this is that the fuel across the country and Europe isn’t the same. Refineries add chemicals to their fuels to help prevent gelling. Fuels that go to the southern regions don’t see the same temperatures as fuel in the north so they don’t see the same amount of protection. Even with additives, fuels may still gel. One thing you can do is add an anti-gel additive to your fuel. These will help stabilize your fuel at lower temperatures but usually only required in the most extreme temperature drops.

Some of us older folks can remember the days of the old school truckers, who used to be seen to light small fires under the diesel tanks of their vehicles to warm up the fuel to prevent the gelling in winter months.

Health and Safety would have a field day if that was seen today !!!



 3, Power and Economy

A down side to this winterisation of the fuel is that the fuel has a lower cetane rating. Cetane is a rating for the fuel’s quality

Image; Eviro-fuel

of combustion. It is actually an extremely important rating to know and one that most of us have no way of finding out. The cetane rating isn’t regulated by any agency and as such, there is quite a big swing between not only brands, but even within batches from the same refinery.


If you have ever filled up somewhere and the motor felt a little peppier or you suddenly got a little better fuel economy out of the truck, that is because the fuel had a higher cetane rating. If fuel stations would start posting the cetane rating, it would be worth driving a few extra miles and paying a little more for a higher rating. Although the rating scale from good to poor is only around 7 points the engine performance difference is significantly noticeable.


The winterized fuel does not provide the same level of performance as the summer fuel, so your mileage will likely drop while using it. A reduced Cetane rating reduces the ability of the fuel to auto-ignite, a process that eventually leads to lower fuel economy. This will cause a drastic drop in mileage on our heavier 4x4s, for smaller diesel cars it is much less, but still there.

There are a few options to consider, which may help your fuel mileage when dealing with winter and a diesel engine.


  • Drive with a lighter right foot.

Poor driving habits can cost you 33% more at this time of year

  • Check your tire pressure.

You can improve your fuel mileage by up to 3.3% by keeping your tires inflated to the proper pressure, and properly inflated tires are safer and last longer.

  • Don’t let your engine idle for long periods of time.

Diesel engines do not like long periods of idle time. It’s a waste of fuel and potentially harmful to your engine. Start your engine, once the ilde drops and it’s reached normal oil pressure, drive it very easy until it’s at operating temp.

Long idle times will clog your DPF system or on the older diesels, can cause issues like wet-stacking.

  • Water separating units

Some vehicles have water separating filters or bowels, others are incorporated into fuel filters. In cold conditions water can enter your fuel from condensation on the inside of half full or empty fuel tanks. Keep you eye on these filter units and drain them regularly, in very cold temperatures they can freeze, expand and split causing fuel loss or air drawn into your fuel system.  I have experienced this on trucks in -12 deg temperatures.


So you are now a little bit “fuel” wiser for the coming winter months, keep the usual winter gear in the boot including a folding shovel & blanket, drive safely and all will be well.



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