DETROIT - In a quest to find a useful outlet for exhaust heat that otherwise goes wasted, BMW and GM are testing methods and devices that could convert excess heat from a car’s motor into electricity, and in turn reduce gas mileage to boot, according to http://tech.blorge.com.

GM has already gotten as far as to build a prototype, which amounts to a small metal-plated device that’s designed to fit around an exhaust pipe. The company predicts that it could improve fuel efficiency in a Chevrolet Suburban by about five percent, or 1 mile per gallon, according to CNet. While this isn’t much, the improvements would be greater in smaller, more fuel-efficient vehicles.

The process involves the technology of thermoelectricity. In its simplest form, it’s the process of using temperature differences to produce electricity. A good example of this technology in use is in “cooled seats” that are appearing in luxury vehicles these days. Thermoelectric researchers at Ohio State University are working with auto companies to develop a method that could improve the efficiency of existing materials by producing an electric current from differences in temperature.

If everything works right, the idea is to use the heat from an engine to produce that electric current, and then channel the energy into a useful form that can be applied to a number of things. It’s estimated that 30-40 percent of an engine’s heat is already used in one way or another, but auto companies are trying to put the other 60-70 percent to use.