Prevent Diesel Fuel from GellingDiesels make up a small portion of vehicles on the roads.  Even including smaller diesel vehicles like trucks, SUVs, personal cars, and heavy-duty trucks together, diesels are a minority.  Most vehicle owners don’t have to worry about temperatures in the winter because gasoline doesn’t change much with freezing weather.  The same can’t be said for diesel fuel.  So how do you prevent diesel fuel from gelling if you’re in colder weather?

When it freezes in the cold winter months, diesel engines won’t start.  Consequently, diesel vehicles often set on the side of the road until the weather gets warmer.  Never heard of gelling, or know why it occurs?  Well, we’ll explain how it happens, and possible solutions to prevent it.

How Does Diesel Fuel Freeze aka Gelling?

Your understanding of how water freezes gives you get the basis of how diesel fuel freezes.  It usually doesn’t freeze to a solid like water does.  Instead, diesel fuel just thickens from a simple liquid to a gel.  If you’ve used hair gel, you know it doesn’t pour very well.  Consequently, something with that consistency doesn’t flow in your diesel fuel system.

Rather than ask how diesel fuel turns to a gel, a better question is to ask why it thickens.  In the United States, petroleum-derived diesel from your local gas station is composed of about 75% saturated hydrocarbons (primarily paraffins) and 25% aromatic hydrocarbons.  You’ve probably heard of paraffins.  They are commonly associated with paraffin wax.  What does wax do at a high temperature? It turns to liquid and flows.  If that wax gets cold?  You guessed it: it turns to gel.  That’s why diesel fuel turns to a gel at cold temperatures.

How Cold is “Cold”?

How cold does the temperature needs to be for diesel fuel to gel?  Most diesel fuels will freeze at common winter temperatures.  Petrodiesel, which is what we typically buy at the pump, freezes around 17.5 °F.  Biodiesel can freeze between temperatures of 35° and 60 °F.  Yes, you read that right.  Diesel fuel can freeze on a warm spring day at 60 degrees.  The viscosity of diesel fuel, its thickness as a liquid, increases as the temperature drops.  The lower the temperature goes, the less diesel wants to flow in your fuel system.

AMSOIL Diesel Fuel Additive to Prevent Diesel Fuel from Gelling

How Do I Prevent Diesel Fuel from Gelling?

Understand and prevent the scenario that causes trouble: temperatures affect diesel fuel.  So, in the manufacturing process, diesel fuel refineries try to prevent diesel fuel from gelling by mixing different variations for winter and summer blends.  They often call them #1 and #2 diesel fuels.  Diesel #1 contains less wax which makes its cloud and pour points typically around 20ºF or colder.  These are better suited for winter temperatures and colder weather.  Diesel #2 includes more wax and is formulated to be best used in the warmer summer months.


When it comes to diesel fuel, there are three usual terms related to viscosity and fuel flow:

  • Cloud Point – On point here, this is the temperature when wax will begin to crystallize in diesel fuel.  It’s normally around 32ºF for #2 diesel fuel, but it can be as high as 40ºF depending on the specific formulation.
  • Cold-Filter-Plugging Point (CFPP) – Similarly, CFPP is the point when wax crystals in diesel fuel will clog the fuel filter.  In layman’s terms, this is what gelling is.  It’s the point where Diesel fuel has become so thick that it refuses to flow through the filter material
  • Pour Point – Finally, the Pour Point is the lowest temperature at which diesel fuel maintains its ability to flow.  Below the Pour Point is where gelling occurs.

The diesel fuel formula bought at the pump meets the weather conditions in your near-term future.  The ultra-low-sulfur diesel (ULSD) much meet CFPP and Pour Point characteristics to protect diesel drivers and their fuel systems.  Although diesel fuel is formulated to handle upcoming weather and seasons, it can’t protect from dramatic temperature swings.  Some of the country can be at t-shirt weather in the afternoon, yet below freezing at dawn.  In these cases, you may have to take it upon yourself to prevent your diesel fuel from gelling.

Be Proactive, not Reactive

An ounce of prevention is worth a pound of cure as the old saying goes.  Accordingly, preventing gelling is easy to do with AMSOIL Diesel Cold Flow.  It’s best to add before filling the fuel tank if possible, and that will offer the best chance for complete mixing.  It lowers cold filter-plugging point (CFPP) by up to 40°F and prevents wax settling in the fuel tank and filters.  And it is safe for use with all diesel fuels. That does include biodiesel.

If you have a normal routine of adding diesel fuel injector cleaner or cetane boost in, you may consider adding AMSOIL Diesel All-In-One into your tank instead. It offers cetane booster, injector and fuel system cleaner, plus the added protection of diesel cold-flow and anti-gelling properties.  Diesel All-In-One is safe for use in all diesel fuels, including biodiesel.  Likewise, it may reduce the cost of adding everything separately.  Plus, it will give you all-season protection without having to become a meteorologist in your spare time.

My Diesel Fuel Gelled.  So, Now What?

The worst-case scenario is when your diesel fuel has gelled.  You’re stuck and your diesel engine won’t start.  What do you do now?  Thankfully AMSOIL offers a product called Diesel Recovery.  It dissolves the wax crystals in gelled diesel fuel.  The end result: it returns the fuel back to liquid form. It also thaws frozen fuel filters.

One 30-oz. bottle of Diesel Recovery treats up to 30 gallons of fuel.  Remove the fuel filter on your vehicle and fill the filter with Diesel Recovery.  Once it’s full, put it back on your vehicle.  Pour the remaining Diesel Recovery in the bottle into your fuel tank.

You should be able to start the engine.  Allow the fuel system to circulate until full power has been restored.  If you need a quicker restoration of power, install a new fuel filter instead of using the existing filter on your vehicle.

Keep your diesel engine well-maintained and protect it from gelling fuel.  Don’t make it complicated.  Choose the right products that make a dramatic difference in keeping your diesel vehicle running smoothly in every season during the year.  Buy Great Oil helps organize and keep track of your complete maintenance costs for your diesel vehicles.  If you’re unsure about which AMSOIL product is best, feel free to drop us a line.  We’ll help with the products that best fit your requirements because we are your local AMSOIL dealer.

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