Just like a diet of junk food can adversely affect a human's health, a diesel tow truck cannot function properly on a diet of improper diesel fuel. International® offers the following advice on what characteristics to look for in diesel fuel No. 2, or DF2, the fuel recommended for use in your International diesel engine, and a good idea for the entire fleet.

Whether you buy diesel at the local station, or you bid for your diesel fuel, you need to know the characteristics of the diesel fuel your buying.

It's important to spec diesel fuel characteristics because not all DF2 fuel is the same. In fact, DF2 has several different properties that are important for the operation and emission performance for your engine. All engine manufacturers and most truck and bus OEM's will spec the fuel because of the need to control engine performance and emissions.

The following six characteristics for your DF2 fuel are what you should be aware of in order to maintain optimum performance of your diesel engine: cetane, lubricity, pour and cloud point, sulfur content and biologic oil content.

• CETANE: The word cetane represents the ignition value of the fuel. Currently the on-highway DF2 has a value from 40 to 55. Most electronic diesel engines require a cetane rating of 45 or higher. Higher cetane values tend to improve the engine's cold-starting performance and reduce white smoke.

• LUBRICITY: Just like a door hinge needs oil to continue working smoothly, fuel must be capable of lubricating the system components in order to prolong the fuel system. Since sulfur content has been reduced in diesel fuel due to EPA mandates, the fuel has lost some of its lubricating ability. It's important to specify lubricity as many fuels available have too little lubricating abilities.

• A test called SL BOCLE will measure the fuels' ability to lubricate and express the lubricity in grams of load. Many engine manufacturers require a minimum SL BOCLE rating of 3,100 grams. The higher the value, the better the lubricating ability.

• POUR AND CLOUD POINT: Pour and cloud point should be tailored for your specific climate needs. The cloud point refers to the fuel's temperature as it begins to thicken and "cloud." The pour point refers to the temperature of the diesel fuel as it thickens 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 and pour point are 20 degrees apart. Normal cloud point often occurs at 40 F and pour point at 15-20 F with DF2 fuel. If you are in a cold climate, use winterized fuel or winter blended diesel fuel, which is a mixture of DF1 and DF2. DF1 has a lower pour point, but also has a lower viscosity, or weight, and is harder on the fuel injectors, which is why blended mixture is recommended for cooler climates.

• Sulfur naturally occurs in most of all crude oils, which includes diesel fuel. Although sulfur does help with lubrication, it also has negative effects to the life of the component and raises emissions. When sulfur burns, it creates sulfur dioxide (SO2 ), which has a bad odor and is a precursor to acid rain.

The EPA has a mandated reduction schedule regarding sulfur content, which is defined in parts per million (ppm). Currently, the allowable maximum is 500-ppm. By 2006, the limit will be 15-ppm. Emission performance is directly impacted by sulfur content. DF2 sold in California already has less than 300-ppm, and a Green Diesel Technology™ bus requires ultra-low-sulfur fuel below 15-ppm. 

• Blended diesel fuels contain some portion of biologic oils such as soybean or cottonseed oil. While biologic oils tend to have low sulfur content, they often have low cetane ratings and can support living organisms in your fuel. Despite this, biologic blends can be used as long as the DF2 still meets your total specifications for cetane, cloud point and pour point, lubricity, sulfur content and the biologic content is no more than 20 percent.

To help the environment and engine performance, International recommends the following characteristics for DF2 fuel.

• Cetane rating of 45 or above; 50 for winter fuel.

• Lubricity of SL BOCLA 3,100 grams or higher.

• A cloud and pour point based on the expected temperatures for your climate.

• Sulfur content in fuel that is less than 500-ppm. A content of 250-ppm is better for the engine and 15-ppm is even better for the diesel engine and the environment.

• Blended biologic oils that are not more than 20 percent by volume.