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How Fuel Efficient is the Chevy Volt?

It looks like there's no way General Motors (GM) can sustain its boast last year that the Chevrolet Volt would get an eye-popping 230 miles-per-gallon rating from the EPA, now that the EPA has assigned a figure equivalent to 99 mpg for the Nissan (NSANY.PK) Leaf.

That's the second time GM has over-hyped the Chevy Volt. There was a flap recently over whether the gasoline engine in the Chevy Volt ever directly drives the wheels. GM had insisted for a couple of years it didn't. Turns out it does, indirectly, at least sometimes. That wasn't such a big deal, in my opinion, but it does tend to show GM is, to put the best face on it, anxious for the Chevy Volt to succeed.

The battery powered Nissan Leaf burns no gasoline whatsoever. The EPA applied a formula equating how much electricity it uses to the energy equivalent in gasoline, to come up with a rating of "99 MPGe," according to Nissan. The "e" is for "equivalent." Retail sales are expected to start next month.

The Chevrolet Volt, which is also due next month, runs on battery power until the battery is depleted. At that point, a gasoline-burning internal combustion engine kicks in, to recharge the battery.

A single mileage figure needs to average that out somehow. The EPA hasn't issued an official mileage figure for the Chevy Volt, but a GM spokesman said it's due soon.

In a separate document, the EPA last month proposed assigning "letter grades," like a report card, for fuel efficiency. At that time, the EPA proposed assigning the Nissan Leaf an "A plus." The Chevy Volt was to get an "A," one notch below the Nissan Leaf.

That suggests GM has some crow to eat. In August 2009, then-GM CEO Fritz Henderson held a press conference in which he touted that fact that using a methodology that was "tentatively" going to be used by the EPA, GM had come up with a mileage figure for the Chevy Volt of 230 mpg. the company even created a smiley-face logo to that effect (shown).

It defies logic that a car like the Nissan Leaf that burns no gasoline could be rated lower than one like the Chevy Volt, which does. If that happened, it wouldn't be the first time that a government ruling was illogical. However, this all sure seems to suggest there's no way GM's earlier boast can stand.

Photos: Nissan, GM