It made national headlines last month when some Bloomington school buses stalled during a subzero stretch, forcing the district to cancel classes for a day. The too-quick-on-the-draw mechanical diagnosis? Biofuel that gelled up in the cold. Fox TV commentator Glenn Beck didn't call Minnesotans bio-fools, but he came darn close, holding up the state's first-in-the-nation biodiesel mandate as evidence of how government screws things up.

"Lawmakers put children's safety at stake because they don't want their buses to run on a politically incorrect kind of fuel," opined the bombastic Beck last Friday.

With Minnesota poised to transition to a higher percentage of biodiesel this spring, it's important to set the record straight on the Bloomington bus issue. Biodiesel wasn't the culprit causing the school buses to stall out. Unfortunately, the brouhaha has given the state's pioneering mandates and the promising biodiesel industry an undeserved black eye.

Minnesota law currently mandates that virtually all diesel in the state contain 2 percent biodiesel. Almost any oil can be used to make biodiesel, according to Ed Hegland, an Appleton, Minn., farmer and chairman of the National Biodiesel Board. In Minnesota, it's mostly made from soybeans, then blended with regular petroleum diesel. Petroleum diesel is the fuel on which most of the nation's trucks, tractors and road equipment run. Minnesotans in particular are long acquainted with regular diesel's drawbacks in cold weather. When the temperature drops below a certain point, wax crystals can form and gum up fuel filters. It's why truckers idle their trucks overnight in cold weather and why many who rely on diesel during the winter switch to a different blend to minimize the problem.

Kelly Strebig, a research engineer at the University of Minnesota's Center for Diesel Research, immediately suspected this common cold-weather problem when he heard about the Bloomington school bus situation. He called right away to see if he could help. Initial information only added to his suspicions. Only one type of bus was stalling out that morning -- a less common model whose flat-nose design meant the fuel filter was especially exposed to the cold.

A well-known Golden Valley firm, MEG Corporation, was called in to investigate. The company's conclusion? Biodiesel wasn't to blame, a finding supported by another testing firm this week. Wax crystals from regular petroleum diesel had clogged fuel filters vulnerable to the cold on the flat-nosed buses. Strebig said that when the filters were brought to room temperature, the substance clogging them poured out. A biodiesel build-up wouldn't have done that, he said.

While MEG has done consulting for the biodiesel industry, the scientist who led the testing is a respected national expert. Strebig said other facts supported their conclusion. Namely, if biodiesel had been the problem, then there would have been widespread problems with the school buses and truck fleets across that state that use the 2 percent blend. There weren't. Even in International Falls, school buses "ran fine" on the day Bloomington buses did not, according to an International Falls school district spokesman.

This May, Minnesota's mandate moves to a 5 percent biodiesel blend, then gradually phasing in 10 percent in 2012 and 20 percent in 2015. Mandate implementation hasn't always gone smoothly. In 2005, when the 2 percent requirement went into effect, quality control problems prompted the biodiesel industry to call for a temporary suspension while it worked with suppliers to fix problems. Biodiesel remains an important tool in the effort to decrease the nation's dependence on foreign oil and reduce air pollution. Independent testing exonerated it in the Bloomington bus situation. The public should continue to have confidence in its growing use.