Some diesel engines sputtered and quit as their fuel filters became plugged with unknown, slimy gunk.

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One northern Wisconsin company, which bought its fuel in Minnesota, said it changed 50 fuel filters in a month to no avail, as its fleet of trucks ran in fits and starts .

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And it must run on diesel five minutes before shutting down to purge the system of grease, which can clog fuel lines, filters and injectors.

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Not changing fuel and air filters.

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On the transportation side, we can rely more on diesel fuel, especially in combination with particulate filters that remove soot.

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