Automakers aim to boost mileage

DETROIT — In a normal year, the 2009 Chevrolet Cobalt wouldn't be any different from the 2008 model, save for a few minor cosmetic changes. But this is far from a normal year.

With gasoline still hovering around $4 per gallon, many manufacturers are making far more than the usual tweaks to cars and trucks between model years to squeeze out one or two more miles per gallon and catch customers who increasingly rank fuel economy as a top factor when buying a vehicle.

Automakers say you can expect more of the same as they roll out new technology without waiting for full vehicle updates.

"Fuel economy is very important," said Greg Peterson, General Motors' vehicle-performance manager for compact cars, including the Cobalt.

"That is one of the drivers in the changes that we made."

In the high-mileage version of the Cobalt and its Pontiac sister, the G5, engineers varied the intake- and exhaust-valve timing to make the 2.2-liter four-cylinder engine burn fuel more efficiently. They arranged with Goodyear for tires with lower rolling resistance, and they changed the gear ratios of the five-speed manual transmission so the engine revs more slowly at highway speeds.

The result: an extra mile per gallon on the highway, boosting the Cobalt and G5 XFE models to an Environmental Protection Agency (EPA) estimated 37 mpg.

GM's competitors also were busy tweaking existing vehicles between model years.

Ford engineers added a six-speed automatic transmission, electric power steering and variable valve timing to the Escape and Mercury Mariner small sport-utility vehicles to get an additional two miles per gallon on the highway.

The four-cylinder, two-wheel-drive version will get 28 mpg, said spokesman Said Deep, yet the 2009 four-cylinder accelerates as quickly as the 2008 Escape V-6.

Changes were made in other models to get similar improvements, Deep said.

Six-speed transmissions, which are used by most automakers, make vehicles more efficient as they start and stop in the city. On the highway, they also require fewer revolutions per minute, increasing efficiency.

Electric power steering reduces drag on the engine by removing the belt that powered the old hydraulic system.

At Chrysler, engineers took similar measures on several models but also recalibrated gas pedals, changed to more efficient air-conditioning compressors and tweaked transmission-shift intervals to make them more efficient.

For instance, Chrysler was able to push the highway mileage of the Sebring and Avenger midsize sedans to 31 mpg, up from 30.

Honda and Toyota, which have led the Detroit automakers in fuel economy in recent years, each said they weren't making similar changes to existing models, partly because they're already using some of the new technology.

"Honda's been a fuel-economy leader for an entire generation because we bake in good fuel economy at the design stage," said spokesman Ed Miller.

The company does make changes to existing vehicles between model years when technologies are developed, Miller said. The Odyssey minivan V-6 engine, for example, was given the ability to work on three, four or six cylinders between the 2007 and 2008 model years, Miller said.

With the U.S. auto market continuing its shift from trucks and SUVs to more efficient cars and car-based crossovers, automakers say they'll keep adding technology from year to year to keep making their cars more efficient.

GM worked within an existing older design on the Cobalt and G5 to drive its mileage to what the company says is a leader among comparably equipped cars in the subcompact class.

And when new models come out, look for more dramatic improvements. GM, for instance, says the Cruze, the Cobalt's replacement coming in the second half of 2010, will get around 45 mpg on the highway.

Although the gains may seem small between model years, they will add up over time, the automakers say.