Why hybrids often deliver lower mpg than advertised
August 16, 2013
by Richard Truett
Because of hybrids' complex powertrains and other factors, the gap between real-world fuel economy and the window label is often greater than it is with vehicles powered by conventional gasoline or diesel engines.
Here are a few factors that can cause these gaps:
Temperature: Winter-blend gasoline contains additives that lower the fuel's freezing point and allow for faster engine warm-ups. Winter-blend gasoline contains less energy than summer blends, causing fuel economy to drop. And drivers in cold weather tend to use more energy-gobbling accessories such as seat heaters, window defrosters and heated outside mirrors.
Vehicle condition: New vehicles with few miles use more energy until the moving parts have a small amount of wear. After about 5,000 miles, vehicles begin to deliver better fuel economy.
Top speed: Most hybrids tend to get better fuel economy in stop-and-go city driving, in which the electric motor does much of the work.
Driving style: To achieve EPA-beating fuel economy, many hybrids must be driven at speeds at or below posted limits, especially on the highway, with the air conditioner off and with careful attention to acceleration and braking.
Full article at link.