What to do if your diesel fuel gels

If you can’t start your diesel after a colder-than usual night, or if the engine is running rough and with low power, you might be experiencing fuel gelling.  Read more about fuel gelling, how to prevent it and what to do about it if it occurs.

Cold weather can be hard on a diesel engine, but as temperatures plunge into the teens-below-zero, diesel owners must also deal with fuel gelling problems.  Untreated diesel fuel will start to gel at just 32 degrees and be fully gelled around 15 degrees.

The term “gelling” means that the diesel fuel literally turns into a hard, paste like wax.  This substance obviously cannot be pumped into fuel lines, pumps or injectors, so the vehicle will not run.  

How to prevent fuel gelling…

Most quality fuel stations will sell a “winterized” blend of diesel fuel in colder months, but, the ability of that fuel to resist gelling can vary widely.  Like most things, it is better to take things into your own hands and use a fuel additive that has anti-gel properties.  Good brands of fuel additives include Opti-Lube, Stanadyne and others like PowerService and Lucas.  For instance, proper dosing of Opti-Lube Winter Formula should survive until -50F/-45C.  


The other thing to pay attention to is your fuel filter.  In addition to holding water, the fuel filter media holds contaminants that have been filtered out of the fuel.  The more contaminants in the filter, the quicker the fuel will gel.  That is why it is always a good idea to put in a new fuel filter every winter – a clean fuel filter will help limit the chances of gelling.

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A dirty fuel filter, left, will gel easier than a clean filter, right.

What to do if your fuel Gels…

While gelled fuel sounds bad, the good news is that diesel fuel will return to normal as soon as the temperature goes back up above the gel point.  Pushing a vehicle into a garage and leaving it for a few hours is typically all that is required to fix the gelling problem.  However, if the temperature is not expected to go back up or a heated space isn’t available, there are some other things you can do.


Opti Lube Gel Melt is designed to fix a gelled fuel tank

There are a variety of products that can be added to a gelled tank that can help return the fuel back to its normal state.  Products like Opti-Lube Gel Melt and Diesel 911 are designed specifically for gelled fuel.  Simply add one of these to the tank, following the dosing instructions.  You don’t need to heat the tank or mix it.  Depending on tank size and design, these can take some time to work.  A big limitation is that the treated fuel in the tank they may not be able to reach gelled fuel that is not in the tank – like in fuel lines and filters.

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Collection of fuel filters clogged with gelled diesel fuel.

If your fuel does gel in the filter, there are a few options.  You can try carefully heating the filter with a heat gun or hair dryer.  If the filter has a cap or a priming screw, try adding some of the Opti-Lube Gel Melt directly to the filter.  If that doesn’t work, or if your filter is sealed, you’ll need to replace the filter – consider always having an extra fuel filter on hand in the vehicle.  Pre-fill the filter with treated diesel fuel – or straight fuel additive – so that the treatment makes it to the fuel pump and lines quickly.


In short, preventing getting stuck with gelled fuel in your tank starts at the prevention stage by buying good quality diesel fuel and using a fuel additive, especially once the temperature drops below 32F.  Being prepared means having a bottle of Gel Melt and an extra fuel filter in your vehicle at all times, just in case you get an untreated batch of fuel or temperatures drop lower than you had expected.

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