New Mariner Hybrid: Nice and green

The Mercury Mariner Hybrid has a 2.3-liter 4-cylinder engine working in tandem with an electric motor and a continuously variable transmission or CVT. Unlike most transmissions which have "first, second, third..." gears, a CVT changes gear ratios in a continuous, stepless fashion.

In this way, the CVT can always stay in the ideal gear ratio rather than being forced to choose the best out of a set of gears.

The downside of that is increased, or at least more noticeable, engine noise when accelerating or going uphill. The transmission allows the engine to stay at one speed, so when needed it spools up to 4,000 rpm and stays there, setting up a grinding roar that resonates through the cabin.

On the quiet side, the Mariner Hybrid can drive at up to 25 mph with its gasoline engine off. (Unless the batteries need to recharge.) That silence is one of the best things about driving the Mariner Hybrid.

EPA mileage estimates for the 2008 Mariner Hybrid and its siblings aren't available yet, but the 2007 version has EPA estimates of 36 mpg in city driving and 31 on the highway. 2008 estimates will be lower because of a new EPA test design. Expect about 27 miles per gallon.