i have a 2002 ml320 53k miles, which has been getting 16-18 mpg and recently dropped down to about 12-15! i havent noticed any performance difference or the truck hasnt been throwing any codes. is it because of 'winter' gas?

Winter or cold weather will ALWAYS lower your mileage... my '96 E320 gets 19-20 mpg during winter and 22-23 mpg during summer, this is all city driving. I can get 30-32 mpg during summer on highways

For many years, " real experts " have been quoting an increase in fuel consumption,during winter months, by as much as 20 %.
1. Cold starts = more fuel.
2. Dragging 100's of pounds of slush around = more fuel.
3. Letting car warm up & leaving it running to keep warm = more fuel.
4. Increased friction in the driveline = more fuel.

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2007 C 230 Sport.