Along with the mechanics of the car, the professional should check that the catalytic converter and other pollution control devices are working properly. The low-emission vehicle is like any other car except that it has technology to reduce tailpipe emissions. Alternatively fueled vehicles, which are powered by a variety of fuels such as compressed natural gas, methanol, ethanol, or electricity, are also becoming more available. Technology and pollution control requirements are providing a greater choice of less-polluting cars than ever before. New vehicles generally pollute less.
Smaller cars are generally more fuel efficient.
Larger engines typically result in lower gas mileage. There should be a hissing sound when you loosen it. Less than 12,000 or 15,000 miles per year of vehicle age is ideal, but well-maintained high mileage vehicles with documented service and repair records may be fine. If you see exhaust for longer than 10 seconds or it is dirty or blue, the engine probably needs repair. This guide contains information about the fuel efficiency of cars and trucks for the current model year.