In the U.S., the highest mpg available on the Sonic is 40 mpg and that is the optional 1.4-liter turbocharged engine. In the U.K., the Aveo has several four-cylinder engine options, including a 1.2-liter gasoline, 1.3-liter diesel, 1.3-liter Eco Diesel, and a 1.4-liter. The highway fuel economy on these engines is 68.9 mpg, 83.1 mpg, 85.6 mpg, and 62.7 mpg, respectively.
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Seemingly every car company has a super-Eco diesel engine in its European lineup, but we have yet to see one in the U.S. We think the time has come for one to show up.