How to Ungel Diesel Fuel

To avoid diesel fuel gelling, consider using winterized diesel fuel in cold temperatures and using a cold flow improver fuel additive.
Written by Melanie Krieps Mergen
Reviewed by Melanie Reiff
Updated on Oct 24, 2022
To avoid diesel fuel gelling, consider using winterized diesel fuel in cold temperatures and using an anti-gel fuel additive.
If you drive a diesel vehicle, the last thing you want to hear on a cold morning is the sound of your engine stalling—particularly if it’s a result of diesel fuel gelling.
So what is gelling, and how do you avoid it? Here with these answers and more—plus tips on how to cut down on your
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Why does diesel fuel gel?

Before determining what you should do if your diesel fuel gels, it helps to understand why and how it happens.
Paraffin wax naturally occurs in diesel fuel. It typically exists in liquid form in your fuel tank, but it can freeze and crystallize in cold weather—an event known as gelling.
This is a problem because those wax crystals can clog your fuel filter and prevent your diesel from being able to pass through the system. If wax gets through the filter, other parts of your fuel system, like the fuel lines, may also experience clogs. 
Of course, if diesel can’t pass through that filter, your engine is cut off from its fuel source, leading to engine stalling.

What to do if your diesel fuel gels

If your diesel fuel gels, how should you respond?
It depends on the situation. Once diesel gelling has already happened, the fundamental goal would be getting your vehicle to a shop or garage if possible, where it would have the chance to warm and thaw. 
De-icer fuel additives can also be used in emergencies if your diesel gels, but keep in mind that they can have varying reliability rates.
In some cases, you might need to enlist some help from
roadside assistance

What temperature does diesel fuel gel?

Different types of diesel will begin forming wax crystals at different temperatures, known as “cloud points”
Different types of diesel fuel have varying qualities with varying cloud points, which can generally fall between -18 and 20 degrees Fahrenheit for No. 2 diesel. No. 1 diesel can generally have a cloud point of – 40°F.
The lowest temperature at which diesel fuel can pass through a 45-micron filter without gelling is called the cold filter plugging point (CFPP). Usually, a filter’s CFPP will fall within a few degrees of the diesel cloud point.
The type of fuel filter your vehicle uses might also impact at what temperature gelling becomes a problem for you. For example, many newer diesel vehicles have filters finer than the 45 microns used for the CFPP standard—meaning wax can build up on the filter more quickly and create gelling problems at warmer temperatures.
According to the Alternative Fuels Data Center, if your diesel contains biodiesel, you might experience gelling at higher temperatures—generally between about 26 and 59 degrees Fahrenheit.
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How to fix gelled diesel fuel with fuel additives

Diesel fuel additives can be helpful for various purposes, like boosting performance, cleaning injectors and other parts, or improving fuel economy and reducing emissions. They can also play a crucial role in avoiding diesel gelling problems.
Fuel additives known as cold flow improvers (CFI) or anti-gel additives can help break down frozen wax crystals so they’re less likely to clog your filter, which can help prevent gelling in the first place. 
While not for everyday use, de-icer additives can also be added to fuel in an emergency situation to help ungel it and return the wax to liquid form.
The amount of fuel additive you should add to gallons of diesel will depend on the product, so read its instructions carefully.
However, before doing so, you should check your owner’s manual for your vehicle’s fuel requirements, including fuel additives, so you know what specifications to look for and what precautions to keep in mind.

How to prevent diesel fuel gelling

The easiest way to fix gelled diesel fuel is to prevent it from happening in the first place.
Here are a few ways you can avoid gelled fuel:
  • Use anti-gel fuel additives: As mentioned above, fuel treatment with an additive can help break down wax crystals into smaller forms so they’re not as likely to clog your filter
  • Use winter fuel: In cold climates, transitioning from No. 2 to No. 1 or winterized diesel when you fill up at the fuel pump in the months leading up to winter can reduce the likelihood that you have to deal with fuel gelling
  • Use an engine block heater: When extreme cold temperatures lie ahead in the forecast, some diesel truck drivers also use engine block heaters to help warm up the fuel before startup

When to see a mechanic

Don't hesitate to contact a mechanic if you’re unsure whether you’re dealing with diesel gelling or another problem. 
Another similar problem to gelling is icing—the difference being that the crystals forming are ice rather than wax. If you suspect there’s water in your fuel system, you’ll want to consult your mechanic as soon as possible to avoid causing severe damage to your fuel system.

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Don’t let gelled-up diesel or a faulty
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