What Temperature Does Diesel Freeze?

Towards the end of the year when the weather changes and it gets noticeably chillier, many drivers begin to worry. Cold weather brings with it unique hazards for road users, often with significant safety concerns.

One question in particular springs to mind for the owners and operators of machinery. What temperature does diesel freeze? 

If you drive a diesel vehicle it’s important that you are aware of what low temperatures will do. This is because diesel can be affected even by relatively mild dips in temperature. “Mild”, in the case of diesel, when compared to gasoline’s freezing point of -100°F (-130°C).

Freezing Diesel

Before we name the freezing point of diesel, it’s important to get some background on diesel as a chemical compound. 

Diesel is a liquid, but it’s obviously different from water. For instance, it will not freeze into a solid mass in the same way that water freezes into solid ice. 

Instead, the paraffins – the most abundant hydrocarbon in diesel – will thicken. This increases the viscosity so much that the engine is not able to process it as fuel. It may even thicken to the extent that it is unable to flow around the engine at all.

All diesel fuels are a mixture of crude oil and biomass. The high paraffin content comes from the crude oil content.

These hydrocarbons are unable to arrange themselves in such a way that they create a new, orderly structure in the manner that water molecules do when they freeze into ice. Because no organized form can emerge, the molecules cannot manifest a strong solid shape.

The absence of this shape and the addition of biomass means that diesel will not freeze solid. It will instead become increasingly viscous until it is a soft, waxy solid. This is called the gel point. 

Freezing Point Of Diesel

Diesel fuel will begin to ‘freeze’ at 32°F (0°C). At this temperature, the paraffins begin to harden and the gelling process of diesel begins. 

At 32°F (0°C), the diesel will become cloudy. You’ll find that you’re still able to drive your vehicle with no issues at this point, but you should note this as a warning. If you notice that your fuel is cloudy or no longer transparent, you need to get your engine warmed up. Let your fuel get any colder and you may be looking at some more serious issues.

If it gets still colder out and the temperature drops to somewhere between 10°F and 15°F (-12°C and -9°C), the wax paraffin will crystalize and the viscosity increases dramatically. At this point the fuel will not flow around the engine and, even if you did get it to move, it will be too thick for the engine to use. 

At this point, your diesel has gelled. Gelled diesel will clog up your fuel lines and your tank. You need to let the diesel thaw out and get back to its proper consistency. Fortunately, gelling and thawing will not impact the efficacy of the fuel.

If the diesel is kept too cold for too long you may find that the fuel lines have been ruptured. At this point, your only option is to take your vehicle to a mechanic to get it fixed.

Freezing Diesel Prevention

Using a fuel additive designed to prevent gelling is the best way to keep your vehicle in proper working order even in the coldest climates.

These additives work by lowering the gelling temperature by almost 40°F (5°C). This temperature difference may not sound like a lot, but it’s likely enough of a change for everything apart from the most extreme weather conditions.

The additive will also prevent any water in the engine from freezing. Since water expands as it gets close to 32°F (0°C), keeping it in liquid form will prevent damage to the more delicate parts of your engine that lack space to accommodate this expansion.

The fuel additive will interact with any crystal formation. It is the crystal formation in the paraffin which creates a waxy, soft solid that makes the diesel too thick. This interaction will put a size limit on the crystals and small crystals have difficulty gelling compared to large ones.

A fuel additive will therefore change the properties of the diesel. In this case, it will let it be functional when the temperature dips below 32°F (0°C).

What if your diesel already gelled by the time you found this blog? Don’t worry! You can still use an additive to get things back on track.

Clear the tank and free up the fuel line to get your vehicle moving again. This will usually involve pouring the additive into the fuel tank and leaving it to break down the gelled diesel. This will take at least twenty minutes (but check with the manufacturer for detailed instructions). 

Once the additive has broken down the gelled diesel back into liquid, you can start the engine. It’s best to leave the engine running idle for a couple of minutes before moving. That relatively brief wait will give the vehicle a chance to warm up and grant the fuel lines time to clear completely.

Cold Weather Prep

The best way to keep your diesel from freezing and to keep yourself safe in the colder months of the year is to be ready. Remember – failing to prepare is preparing to fail!

Firstly, make sure that the battery in your vehicle is at its best. This is especially important if the summer has been particularly warm. Drastic changes in temperature from hot to cold can make your battery vulnerable. Test – and replace if warranted – any battery that reads less than 12.45 volts. Why risk battery problems in the winter on top of everything else?

Another thing to bear in mind is that merely using a fuel additive may not be enough if the weather is extremely cold. If you are expecting temperatures to hit below -30°F (-34°C) you must take additional precautions because the additive alone will not suffice. Keep your car near a block heater or in a heated garage to stop your fuel gelling and clogging up the engine.

Final Thoughts

Diesel fuel will not freeze in the traditional sense, but it will become more solid and waxy once it gets to 32°F (0°C). At this point, the diesel has gelled and is useless until returned to its utilitarian state.

Avoid gelled diesel by using the correct fuel additive or by keeping your car near a heat source. 

Ryan Genkin
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