I guess what surprises me is...

I would have thought that 17 years later they would be getting BETTER mileage, not worse.

2007 C230 2.5L 6 cyl:

Fuel Tank Capacity: 16.4 gal.
EPA Mileage Estimates: (City/Highway)
Manual: 19 mpg / 25 mpg Automatic: : 19 mpg / 25 mpg
Range in Miles: (City/Highway)
Automatic: 311.6 mi. / 410 mi. Manual: 311.6 mi. / 410 mi.

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2012 E350
2006 Callaway SC560