REYKJAVIK, Iceland – Mazda’s fuel-saving stop/start system, marketed as i-stop since its 2009 introduction, will be available overseas on the all-new CX-5 cross/utility vehicle when it goes on sale in early 2012, but the U.S. version will not have it at launch.

That’s because the fuel-economy benefits, based on the U.S. Environmental Protection Agency testing, are not great enough to justify the additional cost, says Robert Davis, senior vice president-U.S. operations.

Despite the delay on i-stop for the U.S., Jim O’Sullivan, president and CEO of Mazda North America, says the technology is coming, and that within five years the entire U.S. lineup could integrate it.

“Within five years, it’s a definite, distinct possibility it could happen,” O’Sullivan tells WardAuto’s at a media event here to drive prototypes of the new compact CUV.

The prospects for stop/start technology depend on consumer acceptance, he says. “Education will be important. There are those people driving the vehicle who might not be comfortable with their engine stopping. Will it restart?”

The best way to overcome the anxiety level, O’Sullivan says, is to phase in the technology and establish its reliability across multiple brands and vehicle types.

Mazda’s new Skyactiv gasoline and diesel engines in Europe will be equipped with i-stop.

In 2010, about 10% of Mazda3s with the gasoline direct-injection 2.0L MZR 4-cyl. engine were sold in Europe with i-stop. For the Mazda5 CUV, the European take rate with that same engine is 25% so far this year, the auto maker says.

Most stop/start systems have an electric motor using the same process as when the engine is started normally, by turning the ignition.

But i-stop injects fuel directly into the cylinder while the engine is stopped and ignites it to generate downward piston force.

The benefit of this arrangement is additional fuel savings, as well as quicker and quieter engine restarts, Mazda engineers say.

A recent test drive of prototype European CX-5s here, all equipped with i-stop, confirms the claim: Restarts are unusually smooth and seamless, with both automatic and manual transmissions and with both gasoline and diesel engines.

As a vehicle comes to rest at a stop light, the Mazda system shuts down the engine and orients the pistons in exactly the correct position to create the right balance of air volumes.

When the driver lifts his foot off the brake or steps on the accelerator, the engine controller identifies the initial cylinder to fire; injects fuel into it; then ignites it, beginning the combustion sequence in the remaining cylinders.

Mazda says this approach ensures the engine will restart the same way every time and will return to idle speed in just 0.35 seconds – roughly half the time of a conventional motor-driven device.

Fuel-economy benefits for stop/start systems vary between 2% and 8% according to different test cycles. But Mazda says its technology boosts fuel efficiency about 10% based on Japanese testing, which emphasizes heavy urban traffic with lots of idling.

In the U.S., i-stop yields a gain of about 3% based on the EPA test cycle, “but real-world it looks like around 7% in local urban areas,” Davis tells WardAuto’s.

The refreshed ’12 Mazda3 subcompact, which goes on sale next month, will integrate the auto maker’s new Skyactiv 2.0L gasoline direct-injection 4-cyl. engine, which boosts fuel economy 15% compared with the engine it replaces.

But the U.S. vehicle will not integrate i-stop initially, Davis says.

tmurphy@wardsauto.com