5 Tips to Improve Winter Diesel Fuel Performance

Diesel specialists from International Truck and Engine discuss fuel choices for top performance in cold weather.

The quality of diesel fuel that owners choose will affect fuel consistency, engine performance, and fuel economy during winter months. Learning about the chemistry and characteristics of diesel fuel will help truck owners make better decisions at the pump, giving their engines the best chance to perform at a high level all the way through the first thaw.

Diesel fuel makeup

First, it is important to understand diesel fuel characteristics. Diesel fuels are derived from middle distillates, petroleum oils with higher boiling ranges than gasoline. Because converting fuel to heat is what creates power from an engine, the higher boiling ranges allows diesel engines to provide more horsepower than their gasoline counterparts. The boiling range, or energy value of the fuel, is measured in British thermal units, which represent the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit. On average, diesel fuel contains 138,000 Btu per gallon, compared to 124,000 Btu per gallon of gasoline. This additional energy contributes to the fuel efficiency diesel engine owners enjoy.

Cetane

This colorless, liquid hydrocarbon holds excellent ignition qualities, and is a term closely associated with diesel operation in cold weather. Fuels are compared to cetane to determine their ignition quality. Higher cetane values improve the engine’s cold-starting performance and reduce white smoke. When diesel fuel first enters the combustion chamber, there is a lag time until the fuel ignites, but that lag time can be shortened with a high cetane number. Most electronic diesel engines require a cetane rating of 45 or higher. In cold temperatures, a vehicle will respond to a high cetane rating with better engine performance, better fuel economy, and better exhaust emissions.

On the other hand, a low cetane fuel (below 40) will cause white smoke, poor fuel economy, and the lack of power in cold weather. Minimally, 40 cetane is desired, and can be found at most fueling stations, but premium diesel fuel (above 45 cetane) will provide increased power and fuel economy. You will not find the cetane number on fuel pumps, but can ask the attendant at your area fuel stations to determine which location carries premium fuel.

Lubricity

In addition to providing energy, diesel fuel doubles as a lubricant for diesel injection equipment, such as rotary distributor pumps and injectors. Fuel must be capable of lubricating the system components in order to prolong the fuel system. Because of the diesel’s dual purpose, the viscosity or weight of the fuel is vital to its performance. In normal temperatures, higher viscosity fuels, such as Diesel Fuel Number Two, or DF2, will perform better than the thinner, lower-viscosity fuels in automotive diesel engines, which can be hard on the injectors. International’s Power Stroke Diesel engine’s electro-hydraulic fuel system design is much less vulnerable to lower lubricity fuel than mechanical systems. And this bodes well for the vehicle’s performance in cold weather.

A test called SL BOCLE, which can be performed at your local International dealership, will measure the fuel’s ability to lubricate and express the lubricity in grams of load. Many engine manufacturers require a minimum SL BOCLE rating of 3,100 grams, and that is the common rating found at diesel fuel stations. The higher the value, the better the lubricating ability.

Cloud point and pour point

As the temperature drops, diesel fuel will thicken. It is important to purchase diesel fuel with a high cloud point for cold weather operations. The cloud point refers to the temperature at which diesel fuel begins to thicken and cloud. The pour point refers to the temperature as it thickens further and will no longer pour. Some engines will fail to run at the cloud point, but all engines will fail at the pour point. Usually, the cloud point and pour point are about 15 to 20 degrees apart. Both points vary greatly, but generally, fuels reach the cloud point at 40 degrees F, and the pour point is reached at temperatures below 20 degrees F.

Winterized fuel

To maximize power and prevent gelling in the winter months, a blend of DF1 and DF2 (winterized fuel) is recommended because it contains far less paraffin, a substance naturally found in diesel fuel. High amounts of paraffin will crystallize at the pour point and clog your filters, crippling your engine. DF1 contains less paraffin that DF2, but it also produces less heat, causing an engine’s power and fuel economy to suffer slightly. Using a mix of the two fuels will balance your diesel engine’s power and fuel economy with the confidence you gain knowing that your engine is protected from wax formation throughout the winter.

Reprinted from Better Roads Magazine
August 2002

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