The new ultra-low sulfur diesel fuel required by all 2007 engines may be more susceptible to waxing during periods of cold weather, according to one industry expert.

An article titled "ULSD on the Road" in the Winter 2006 issue of Fleet Owner, points out that the reduction of sulfur to 15ppm in the new fuel means the paraffin content is higher. Tom Weyenberg, global business manager for diesel fuel additives at Lubrizol, says, "What causes diesel fuel to 'wax' or 'gel' at colder temperatures are paraffin molecules. As a result of the de-sulfurization process … there are more paraffins in ULSD compared to standard 500ppm diesel."

The article notes that kerosene is typically blended with diesel fuel to improve its cold-weather flow characteristics and prevent wax crystals from plugging fuel filters and shutting down engines. That isn’t possible with the current kerosene because it contains too much sulfur, and the resulting mixture would exceed the federal requirements and may void the engine warranty. A new ultra-low sulfur kerosene is needed, but it isn’t widely available yet.

Departments that expect to receive vehicles with 2007 engines should contact their fuel suppliers to determine what steps are required to avoid cold-weather waxing problems. In some cases, blended fuels may be available. In other cases, departments may have to use fuel additives or rely on fuel heaters.