Over the past several months, Minnesota contractors have reported significant fuel filter problems in some of their diesel-run vehicles, possibly linked to the introduction of Ultra-Low-Sulfur Diesel (ULSD) on the market last October. Fuel refineries began producing ULSD last fall as part of a mandate by the U.S. Environmental Protection Agency to reduce the maximum sulfur content in diesel fuel by 97 percent. All diesel fuel is mandated to meet the ULSD standards by 2010, but producers were required to start converting a portion of their supplies to the cleaner fuel last year. By October, most Minnesota gas stations had already made the switch, as producers saw little benefit in manufacturing multiple diesel strains. Hoon Ge, a Wayzata-based fuel consultant who analyzed 30 fuel filters that failed last month, said he believes most of the problems are linked to two unintended side effects from ULSD.

The good news is that one side effect should only be a problem in extreme cold. But the other is likely to get worse when summer arrives. The cold snap blues The frigid weather that hit the region last month caused many fuel tanks to reach their "cloud point" - that is, the temperature when small waxy crystals begin to form suspended in the fluid. It's an effect especially pronounced among heavy off-road vehicles, which tend to sit outside on construction sites and often lack tank heaters. A "cloud" effect is nothing new or worrisome, but unlike traditional diesel fuel, the ULSD doesn't produce a uniform cloud throughout the tank. "It seems that when those paraffin wax crystals form, they immediately fall to the bottom of the tank," Ge said. "Then when they start getting into the filter, the pump fills up with wax and stops. " Of the failed filters Ge analyzed last month - which were supplied by Minnesota Weights and Measures and the Minnesota Petroleum Marketers Association - 30 percent showed evidence of paraffin wax build-up. Ge and his company, MEG Corp., concluded that the unusual wax appears to be a result of the sulfur-removal process. Fuel producers inject diesel with hydrogen to extract the sulfur, but they may be removing other substances as well that alter the fuel's chemical structure. As a result, some of the freeze-resistant additives that drivers pour into their gas tanks in extreme cold are less effective on the new diesel. "The problem really jumped to the fore in that cold weather snap," when temperatures remained consistently below zero for more than a week, said Tim Worke, director of highway and transportation for the Associated General Contractors of Minnesota. If warmed to room temperature, the waxy substance melts. But the below-room-temperature winters throughout the northern United States are enough to warrant concern in the construction industry. Surprisingly, the Minnesota Truckers Association has reported fewer problems than AGC or the Minnesota Department of Transportation. While truckers expose their vehicles to frigid conditions, they keep their engines running most of the day and don't allow the paraffin wax time to build up. It would seem that the simple solution to the wax build-up is for contractors to run their vehicles more when polar weather hits - an already common practice designed to prevent icy build-up if water in the fuel should separate and freeze. Warmer weather, however, could bring about another foil for fuel filters. Warm weather woes As Ge is quick to point out, a number of diesel engine problems began last fall, months before the cold hit. About one-quarter of the filters MEG analyzed were coated with a dark greasy substance that wasn't affected by temperature. As it turns out, sulfur in fuel tanks provides an unintentional benefit by killing off microbial bacteria that naturally grow inside. Without the natural biocide, vehicle owners will have to clean their tanks on a regular basis or risk bacteria growth. Contractors in the southern United States have reported more bacterial blockages than in the Midwest, as the bacteria thrive in warmer weather. "We want everybody to be proactive, or they're going to have microbial problems," Ge said. "It's probably going to grow faster in the warm weather, so it's critical that they at least check their tanks quarterly ... The time when you would go for 30 years without cleaning your tank is over. " MEG is currently working on a new chemical additive for Indiana-based Fuel Performance Solutions that could serve as a bacteria-killing substitute for sulfur. If everything goes well, Ge predicts fuel distributors may be able to add it to their supplies by the end of the year. "Preliminary studies indicate that it's very promising," he said. Concern spreads The extent of the problem is not yet clear. An informal meeting to discuss the issue last month unexpectedly drew a crowd of dozens, including representatives from MnDOT, AGC Minnesota, Ramsey County, the University of Minnesota and a number of individual contractors and fuel suppliers. Last week, AGC distributed a fuel complaint form to its members to assess just how widespread the blockages have become. "Rather than anecdotally complain, we need to collect data," Worke said. "We're just trying to get our arms around it. " But it may be difficult to get a handle on how many problems might be linked to ULSD, as contractors face mechanical challenges all the time. For example, some contractors who reported filter issues originally chalked them up to improperly blended biodiesel, which last winter had caused a rash of similar complaints. But only one of the filters in MEG's analysis showed any signs of such a problem. "The main issue we had last year was a high level of glycerin in the bio part of the fuel. But we pretty much got that problem resolved," Ge said. "The producers have to do quality testing on every batch they make now. " Regardless of how many contractors it affects, problems with ULSD could crimp auto sales if they aren't addressed soon. Fuel-injection systems in trucks have undergone several changes in the past decade, and fuel filters have become finer and finer as a result. Whereas the holes in a filter used to be 10 to 30 microns in diameter, they now start as low as three microns. When paraffin wax or microbial bacteria begins to form in these newer fuel tanks, they could clog the filters more quickly than old ones - and distrust of the newer engines is beginning to spread. "Everybody's already scared about buying 2007s," Ge said. Tony Frattalone, of St. Paul-based Frattalone Cos., said he sees a hesitancy to buy new among his construction industry peers. "The older the better," Frattalone said. "This stuff just starts collecting, and it clogs them up faster; and the older ones actually seem to have an easier time. " Paul Schmokel, vice president of sales at Hallman Oil in St. Paul, has seen the same thing. "The guys who had to buy [new vehicles], bought. The others are hanging back and waiting to see what happens at this point," he said. Every person interviewed for this story emphasized the benefits of cleaner fuels and didn't want to be misconstrued as pro-pollutant. But they're seeing a growing concern about Ultra-Low-Sulfur Diesel, and they believe that some of the fuel's unexpected side effects may still need to be worked out. "Everybody sees these changes coming, and the industry [members] want to position themselves to be ready for this," Worke said. "But they also don't want to be guinea pigs. "