What happens to diesel fuel in cold weather?

For many, owning a diesel-powered vehicle is not just a point of pride, but also a means to a living. Diesel vehicle owners count on these powerful workhorses to provide the necessary torque in heavy-duty applications.

The higher energy content of diesel fuel provides more power and fuel economy in most vehicles compared to their gasoline-powered counterparts.

"In winter the tables turn in favor of gasoline vehicles as diesel fuel tends t gel when temperatures drop."

Gasoline and Diesel fuel: the same, but different.

Diesel fuel, like gasoline, is a mixture of many different components combined to make a desirable “concoction” of combustion. In addition, much like gasoline, diesel comes in an array of grades that may or may not use of bio-fuel components.

Both have grades.

For example, gasoline is separated by octane number for “87 regular”, “89 plus”, or “91 premium” grades of fuel.

Diesel also has different grades, primarily classified as #2 diesel (regular) and #1 diesel (premium). It is further separated for tax exemption purposes as “ON-ROAD Diesel” or “OFF-ROAD Diesel”.

Off-road diesel is often dyed red and to be used only by construction or agricultural equipment that does not regularly make use of tax-dollar pavement. Heavy fines await anyone caught using off-road fuel in a normal on-road vehicle.

Diesel is heavier.

The key difference between gasoline and diesel is the range of components make up each of these energy sources.

Molecules in diesel are much larger and compact well against each other, making them quite dense.

On average, one gallon of gasoline fuel weighs about 6.2 pounds. Diesel fuel however, tips the scales slightly more at 6.9 pounds per gallon average. Denser fuel = more energy, sounds simple enough! It is this characteristic of “compaction” however, that becomes the undoing for diesel fuel use in cold weather.

Diesel freezes.

Frozen diesel

When temperatures drop, the bonds between diesel fuel molecules become more rigid and they begin to bind strongly. The process continues until thin sheets of diesel are bound together forming a waxy substance within the fuel. It may be first noticeable by a slightly hazy appearance within the fluid.**

Over time, enough of these wax bits become clogged in fuel filters and prevent the flow of fuel. If the process continues further, the fuel may gel completely forming a semi-solid of waxy goo. In this state, the fuel can no longer flow to the engine and the vehicle is unable to run!

The term “gelled” is a commonly coined phrase for inoperable equipment in cold environments. Frozen water molecules in diesel fuel aid in the wax formation process by giving the wax a template to build on. Biodiesel blends tend to hold greater water content more readily in suspension and further exacerbate the effect.

Diesel fuel requires year-round maintenance: especially in the winter.

Once a fuel source begins the formation of wax and gel, there are few options to undo the process. There is no pour-in-the-tank product that can quickly and effectively dissolve already gelled fuel.

1. Prevention
By far the best method is preventing wax and gel formation before cold temperatures arrive. Anti-gel additives prevent the formation of wax layers and gel formation by inhibiting diesel fuel binding to itself. Many additives inhibit the formation of waxes in diesel fuel, allowing the fuel to flow freely well below typical untreated operating temperatures. The repetitive pattern which diesel wax forms can be interrupted to keep fuel fluid, and wax particles small.

2. Mix the cold fuel with high quality #1 diesel or kerosene
Ideally, this would dissolve the wax. This method is quite costly, and usually requires large quantities of fluids for the desired effect. Using mixtures of #1 Diesel or Kerosene also lead to reduced fuel economy as they contain lower energy content.*

3. Heat
Constant heating of the fuel can effectively melt diesel fuel wax and restore flow. Large amounts of fuel can take time to heat and is often difficult to do in cold weather. Most diesel vehicles have a heating element in or near the fuel bowl filter to assist the melting process.

However, many times the filter is overcome with wax faster than the heater can handle, leading to engine stalling and shutdown. Discarting and replacing the fuel filter is often necessary to restore fuel flow when gelled. If the vehicle will run long enough to warm up, often it will generate enough heat to stay running.

The temperature at which fuel gels depends on many factors, including seasonal changes. Normally suppliers of diesel don’t want their fuel to gel up so they take a few steps to prevent that from happening. Often it is usually not enough.The potential for diesel fuel to gel can be substantially lowered using anti-gel additives. Combined with optimal blending of light diesel fuels, equipment can start and function in extremely inclement weather.***

BG has a diesel solution!

BG has several diesel fuel additives that greatly inhibit the formation of wax formation and gelling. Here in Kansas, we can see temperatures near zero degrees Fahrenheit in the winter.

I regularly treat the fuel in my diesel truck with BG DFC Plus® with Cetane Improver, PN 248, and have yet to see my truck gel. A few friends of mine in Minnesota prefer BG DFC Plus® HP Extra Cold Weather Performance, PN 238, and have had no issues this winter despite -35 degree temps.

Clint "Chemist" Meyer's top picks for anti-gel

By augmenting diesel fuel with additives from BG, equipment owners can reap the benefits of this energy-dense fuel source in any climate. I’ll talk more about that in my next article.

With chemistry, there is always a solution.

By Clinton J. Meyer
Technical Service Representative
ACS Certified in Chemistry and Biochemistry

References used for this article:
* Reynolds, Robert E. Changes in Diesel Fuel; A Service Technician’s Guide to Compression Ignition Fuel Quality. 2007. Print. Online document. 

**Auroux, Aline. Calorimetry and Thermal Methods in Catalysis. Springer-Verlang Berline Heidelberg 2013. Print.

*** Alleman, Teresa L. and McCormick, Robert L. Biodiesel Handling and Use Guide (fifth Edition). U.S. Department of Energy: Energy Efficiency & Renewable Energy. DOE/GO-102016-4875. November, 2016. Print. Online document. 

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