Ford will offer an auto start/stop system as an option on the 2013 Fusion later this fall. The fuel-saving feature is popular in Europe and is just now beginning to appear on gasoline-powered U.S. models.

While auto start/stop systems are nothing new -- during stops, they shut down the engine and quickly restart it when the brakes or clutch is released -- they've yet to catch on among nonhybrid cars in America. Ford is hoping at least some buyers will spend an extra $295 for it on the SE trim, the company's most popular -- and soon to be the most fuel-efficient nonhybrid Fusion on sale, featuring an estimated 37 mpg highway rating.

The automaker estimates city fuel economy will increase by up to 10 percent and overall economy by 3.5 percent compared with a Fusion without the system. The SE features a turbocharged version of the 1.6-liter 4-cylinder engine used in the subcompact Fiesta.

While official EPA numbers aren't out yet, we're betting the 2013 Fusion SE equipped with the auto start/stop feature will return 28 mpg city and a combined rating of 32 mpg, based on current ratings of the SE's 2.5-liter 4-cylinder and the Fiesta's naturally aspirated 1.6. Taking into account an average 15,000 miles per year, the EPA's standard weighting on combined fuel economy and Ford's own 3.5 percent estimate, the option should save most drivers just $66 per year in gas, at today's regular average of $3.93. That means that buying the almost $300 option will take about 4.5 years to pay you back at the pump.

However, that's just the average. If your commute involves more stop-and-go crawls, or you take plenty of city trips, the savings could be much greater -- and add up quicker. That's also not accounting for what this system could mean in savings when gas prices spike to the sky, as they last did in 2008.

But the relatively low cost and payback times aren't the real issue, Ford says. It's convincing nonhybrid buyers that their cars aren't stalling.

"Our biggest challenge will be getting costumers used to it. The idea of the engine stopping is a little uncomfortable to people," Ford spokesman Mark Schirmer says.

That's why so few automakers offer the feature on their regular U.S. models. Among those that do are the Porsche Panamera and Cayenne, the new BMW 3-Series and several Mercedes-Benz AMG models. On most of these cars, the start/stop system is off by default and has to be switched on by the driver -- a task that can be difficult to even notice, for example, on the Cayenne's button-crazy dashboard. Ford says that it will program the system to remain on at every engine start.

The company launched the auto start/stop system on European Focus models last year and will be adding the option to more 4-cylinder U.S. Fords such as the Fiesta and Focus soon, Schirmer says.

[Source: Ford]