If you operate in the northern half of the United States, diesel winterization should be a priority to keep you moving through the cold season. Not properly winterizing your diesel is simply not preparing for your operating environment, much the same as not having chains or the wrong seasonal clothing. At certain temperatures, diesel will turn into a gel-like substance that will not flow through your fuel system. It not only gels in your tanks, but also in your fuel lines and fuel filter. It can stop you in your tracks, prevent you from getting moving in the morning, and prevent you from getting heat in your cab/sleeper, which presents a serious safety hazard.

It is very difficult to pinpoint a specific temperature at which diesel gels because so many variables come into play. Here, I’m referring in general temperature ranges. There are basically two temperature points that concern us:

  • First is the cloud point, which is the point at which paraffin wax just begins to precipitate out of the fuel. The fuel will start to become cloudy but the actual temperature can vary somewhat. 
  • Second is the pour point which is also referred to as the gel point. This is the point at which so much wax precipitates out of the fuel that it no longer flows. The gel point is generally ten to fifteen degrees below the cloud point.

Let’s take a look at the different types of crude oil, diesel and their temperature characteristics. All petrodiesel contains paraffin waxes, which are straight- and branched-chain hydrocarbons. It’s these waxes that become solid at lower temperatures. The amount of paraffin wax in your diesel depends on the type of crude oil used and the process to manufacture the fuel. Crude oil is typically classified as:

  • Brent Blend: which is broken down into Brent Crude and Brent Light Sweet Crude. 
  • West Texas Intermediate: also known as Texas Light Sweet. 
  • OPEC Reference Basket: which is broken down further as Bonnie Light, Arab Light, Basra Light, Saharan Blend and Minas. 
  • Dubai Crude.

Diesel fuel comes in two blends: summer and winter. For the purpose of this discussion summer blend diesel is non-treated diesel. In this case the paraffin wax will begin to precipitate out as the ambient temperature drops below +32F. As the ambient temperature drops below 0F, the solidifying wax particles combine into solids large enough to be stopped by filters. Summer blend diesel, also called #2 ULSD, will cloud and gel at higher temperatures than winter blend #2 ULSD, which is a mixture of #2 ULSD and #1 diesel/kerosene. It is the kerosene that lowers the gel point in winter blend diesel. The actual temperature at which your winter blend diesel will gel depends on the specific mixture you purchased. The higher the kerosene content, the lower the gel point. For example, the winter diesel in my town is only winterized to +10F and below that, anything is fair game. Some areas may winterize down to -20F. It has not been my experience that the temperature to which diesel is winterized is published near the pump. Typically this information will take a little research.

If you happen to be fueling in a part of the country that is running a petrodiesel/biodiesel blend then you should be aware that biodiesel will gel at a higher temperature than petrodiesel. Biodiesel comes in B2, B5, B20 and B100. That number represents the percent of biodiesel in the mix. Similar to petrodiesel, the approximate temperature at which pure biodiesel will gel depends on the oil it’s made from. Some typical oils include peanut, corn, soy, coconut, olive and canola. Biodiesel from canola oil has the lowest gel temperature. A petro/biodiesel mix will have a lower gel point than pure biodiesel. A petro/biodiesel mix can be treated to lower the gel point just the same as petrodiesel.

All diesel has water suspended in the solution. This water comes from condensation that forms on the inside of a cold fuel tank that has warm fuel. You can also get condensation from temperature and humidity changes. Keeping your diesel as “dry” as possible by using a water separator is a good way to pull the water out of your fuel. As the temperature drops and the paraffin wax begins to precipitate out of the fuel, the water held in suspension will begin to form ice crystals that can cause excessive wear and damage to your fuel system and engine components.

There are several ways to prevent diesel clouding and gelling. I’ve seen insulated fuel tank blankets used in some climates. The most common is to add a winter fuel additive. There are additives to address the moisture content by helping to “dry” the fuel, there are additives that lower the gel point of diesel fuel and there are combination additives. There are even additives that will thaw your diesel after it has gelled, but that can be somewhat difficult on the side of the interstate with the temperature in the teens or below as it requires removing the fuel filter, sometimes more than once. The method you choose is your preference. 

Most truckstop chains treat for the conditions of the region they are in. Check with your engine manufacturer to get their recommendations on fuel treatments, as some can cause damage to the new high pressure common rail injection systems.

The point is to be prepared ahead of time and if you are operating in cold climates it might be wise to treat your fuel. It is much cheaper than a tow and recovery bill. It is also worth noting that it’s possible to buy fuel in a relatively warm climate in the morning and finish your day in a cold climate. Be prepared and proactive in keeping your diesel flowing.

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