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  • Gelling occurs when diesel is exposed to cold temperatures.
  • Diesel typically gels when it’s exposed to low temperatures, somewhere between 10°F and 15°F.
  • To ungel diesel fuel, you can either replace the fuel filter or use a de-gel product.

Every car owner knows fuel is meant to be liquid and not a waxy or gel-like substance. Unfortunately, diesel can turn into gel at certain conditions, which is one of the last things you want to happen.

Why Is Your Diesel Fuel Gelling?

Just like water turns to ice when it’s freezing, diesel turns into gel when it’s exposed to cold temperatures. Diesel contains a waxy substance called paraffin, which can solidify and cause the fuel to turn into a thick, sludgy gel that won’t flow well through your fuel pump, fuel lines, and fuel injectors.

What Temperature Does Diesel Gel?

Diesel typically turns to gel when constantly exposed to low temperatures of 10 to 15°F, but issues can arise as soon as the temperature drops to 32°F.

Ultimately, how fast your fuel gels and at what temperature will depend on the source and quality of your fuel. For example, biodiesel fuel gels at higher temperatures than conventional diesel.

Can Diesel Freeze While Driving?

The simple answer is yes. Diesel can still gel even if your vehicle is running smoothly. While the engine certainly runs hot and warms up other parts of your vehicle, it isn’t always enough to stop your fuel from gelling.

In most vehicles, the fuel tank is located far from the engine, where the warmth of the engine won’t be able to do much.

Symptoms of Gelled Diesel

If you live in an area with a cold climate, then it’s only natural to worry about your diesel fuel suddenly turning to gel. Fortunately, you don’t have to constantly worry because there are a few signs that’ll tell you whether or not your fuel is gelling, such as the following:

Engine Won’t Start

Dealing with an engine that refuses to start? You might have gelled diesel in your tank. When diesel fuel gels, it can clog the fuel lines and fuel filter, effectively blocking fuel from passing through to power the engine.

Sluggish Performance

Has your vehicle felt sluggish in the cold? If the answer’s yes, then there’s a big chance that your diesel fuel is starting to gel.

When your fuel tank’s temperature drops low enough, diesel will start to thicken and cause your vehicle to feel sluggish and accelerate slowly.

How To Ungel Diesel Fuel

If you’re dealing with gelled diesel fuel, then you’re going to want to address the issue as soon as possible, especially since you likely won’t be able to use your vehicle until you do. Here are some tips to fix your gelled fuel:

Replace Your Fuel Filter

If your diesel fuel has turned to gel, it’s likely reached other places too. After inspecting your fuel tank, check on your fuel filter for gel-like particles too. You might have to replace it and drain your vehicle’s water separators as well.  Make sure to wear thick safety gloves to protect your skin from the bacteria that can grow in diesel fuel.

Use a De-Gel Product

Your best bet to fixing gelled fuel is going to a mechanic. If you’re too busy to drop by one, you can try using a de-gel product first. Be sure to buy a de-gel product and not an anti-gel product since the latter won’t work on already gelled diesel.

How To Prevent Fuel From Gelling

Dealing with gelling fuel can be a hassle, which is why it’s a good idea to do everything you can to prevent it. Here are some tips on how to prevent your diesel fuel from gelling:

Use Winterized Diesel

You can ask your local gas station if they have winterized diesel. Not every gas station will have it, but some have a type of diesel fuel with a lower gelling temperature.

Use Anti-Gel Additives

You can also try using cold flow improvers or anti-gel additives to prevent your diesel fuel from gelling over the winter. Anti-gel additives are different from de-gel products, which you add after the diesel has solidified.

Cold flow improvers are meant to prevent your diesel fuel from gelling, so you’ll have to add them while your fuel is still liquid.

Park Your Vehicle in the Garage

Leaving your vehicle outside when it’s cold increases the chances of your diesel fuel gelling, so if you can, keep your vehicle parked in your garage or an indoor parking lot as much as possible.

Use an Engine Block Heater

You can also invest in an engine block heater, an electrical device you plug into your engine to keep it warm even when you aren’t using your vehicle. You can purchase one specifically fitted to your vehicle at your local dealership.

Keep Your Fuel Tank Full

Having more fuel in the tank makes it less likely for water or condensation to collect and cause your diesel to gel. It’s best to keep your fuel tank as full as possible, but keeping it at more than half full should be good enough.

About The Author
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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