What Happens to Diesel Fuel in Cold Weather?

It happens every year. Winter sneaks up on us before we realize that what feels like two weeks of summer has passed. With those freezing temperatures, it is important to understand what happens to diesel fuel in cold weather.

Having a basic understanding of how diesel fuel reacts to the cold will help keep your diesel engine safe from harm. That way, you can keep right on trucking through the winter knowing your vehicle will hold up.

What Makes Diesel Fuel Different?

Just like regular gasoline, diesel is comprised of several ingredients and comes in different grades of fuel for use in different kinds of vehicles. These include agricultural, construction, and transit vehicles.

What sets diesel apart from gasoline is that it is a heavier fuel. It is denser on a molecular level to create more power for the engine it flows through. All things being equal, the same amounts of gasoline and diesel will not weigh the same in terms of pounds.

While diesel delivers a vehicle that extra boost of power when needed, this dense, heavy fuel has a downfall and that is cold weather.

What to Expect from Diesel Fuel in the Cold

As temperatures drop to the freezing mark and below, diesel fuel begins to be affected. It starts by forming solid bonds molecularly. These bonds can become visible as there are more of them, giving the fuel a hazy appearance. This is the paraffin wax in the fuel solidifying. Under normal conditions the paraffin wax acts as a lubricant and maintains the fuel’s viscosity.

As more wax solidifies over time, it can clog a fuel filter blocking the flow of fuel to the engine. As you can guess, the result is a starved engine that will not run.

This problem is commonly referred to as a “gelled engine” and the process of diesel fuel freezing in this way is enhanced by water molecules in the fuel itself. The frozen water molecules provide a base on which the waxy build-up can form, creating a clumpy mess within your motor.

Once this process begins, it can’t simply be reversed with a fuel additive that you pour in the tank to dissolve the gunk away. That is why diesel fuel itself needs to undergo maintenance all year around. You are not getting the exact same product from the pump in June as you are in December.

As most diesel fuel providers blend their fuel starting in the fall, it will already be winterized for use in the cold weather. The fuel is thinner and flows easier, so gelling is less likely to occur. Although the lower cetane value in the fuel also reduces your vehicle’s power and fuel efficiency, the treated fuel will keep your vehicle running.

What can be done to if you have a Gelled Engine?

Even after an engine has suffered through a diesel fuel gelling, you can still get your vehicle running again. There are a few things you can do:


Just like anything else that freezes, turning up the heat in an around your vehicle can melt away the wax buildup to restore the fuel flow through the engine. Although it can take some time to effectively melt a large amount of fuel. Many diesel vehicles have a heating element built in that can help the melting process. When a fuel filter has built up too much wax for melting to take care of it, it’s time to replace the filter to restore proper flow. Often, once the engine is running again, it will generate enough heat to keep the fuel flowing and continue running.

Mix in high – grade diesel or kerosene

Although it will work to dissolve the wax buildup, this method can be quite expensive. A large quantity of new diesel or kerosene is needed to achieve the results. Also, fuel economy will be reduced while these fluids are in the engine.

What can be done to prevent Fuel Gelling?

Fuel additives

Aside from the winterized fuel at the pump, adding anti-gelling additives before the freezing weather arrives can help prevent that wax from forming in the first place. These additives keep the diesel fuel from binding to itself and creating the wax, so it stays flowing even well below the freezing mark. Remember to use fuel conditioners that are diesel specific and not alcohol based, otherwise, you could be straining your fuel system.

Engine check

Giving your engine a routine mechanical inspection can help in preventing fuel gelling. XL Mechanical provides these services to our Red Deer area customers regularly. Checking and topping up all fluid levels. Go over the axels, the transmission, all the pulleys, and the serpentine belt. Replace anything that shows signs of wear. A review of the cooling system, hoses and antifreeze, is also important.

Battery check

Make sure your battery is clean and replace any terminals that look suspect. This includes the positive cable attached to the starter, so you can be sure to avoid starting problems. Of course, a battery charge test is also useful. If you have to replace your battery, it is better to do it on your terms rather than when you need to get somewhere, and your vehicle will not start.

Other common vehicle checks

This applies to every vehicle, not just those that run on diesel. Making sure your wipers are in proper working order, your spare tire is fully inflated, and your moving compartments, like doors and hinges are lubricated will all keep your vehicle running efficiently over the winter. Do not forget about your braking system too.

One Last Tip

Even after all these checks and solutions, it is important to note that a diesel-fueled vehicle needs time to warm up each morning on those cold winter days. Give yourself some extra time for the vehicle to run idling so it can maintain that warm flow of fuel.

Be  prepared and follow the rules of diesel fuel maintenance, and your vehicle can get through winter purring like a kitten. Then you get to do it all over again after another short Alberta summer.