With fuel prices in such flux these days, everyone wants to get the best gas mileage possible.

As a solution to the problem of how to increase fuel efficiency, full hybrid vehicles exploded onto the automotive marketplace, and they gradually spawned mild hybrids. But what's the difference between the two types?

A hybrid vehicle is any kind of vehicle that uses two or more propulsion systems. A mild hybrid has an oversized starter motor that turns off the engine when the car is coasting, braking or stopped, then restarts the motor quickly and seamlessly. A full hybrid has an electric motor and a rechargeable battery, which can work independently or in conjunction with each other.

Mild hybrids don't have hybrid drivetrains (electric motors that start the vehicle), battery storage or the same fuel economy as full hybrids. Rather, their enlarged motors spin the engine to speeds of 20 to 30 miles per hour before injecting any fuel.

If these vehicles have an electric motor, its only functions are to serve as a power booster or starter-generator, or both. Electric motors in these vehicles can't propel the car forward on their own.

Although they do not offer all of the benefits of full hybrids, mild hybrids provide a fuel efficiency improvement of 10 to 15 percent over conventional vehicles because they're not burning gas when stopped. Also, their purchase price is cheaper than full hybrids, and they weigh less than their full counterparts.

Full hybrids boast more sophisticated technology than mild hybrids, such as a battery that stores energy generated from the gasoline engine or, during braking or coasting, from the electric motor. Since the battery actually powers the vehicle at low speeds, it's larger and holds a lot more energy than batteries used to start conventional vehicles.

A full hybrid can propel the vehicle solely on its electric motor, without running the conventional engine, typically during very light cruising and light acceleration. As soon as additional power is needed, the internal combustion engine kicks in, providing full power.

Full hybrids get much better total gas mileage than mild hybrids, plus much better city mileage, since the electric motor is utilized more often in city driving.

Whether you're interested in a full or mild hybrid, there's good news for all hybrid shoppers: Both types may qualify for a government tax credit. However, keep in mind that the credits will phase out as soon as each automaker's hybrid models reach a specific number of sales. Read more about hybrid incentives. Or for more information on hybrid vehicles and driving green, visit our Going Green Lifestyle Center.


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Jaime Grimes


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