These days, when a product promises to improve gas mileage by as much as 60 percent, it gets your attention.

That is why we were drawn to the Hydro 4000, a fuel cell that was sent to us by a company called Green Machine Solutions out of Jupiter, Florida.

The Hydro 4000 promises improved gas mileage from 20 to 60 percent.

You may have seen these products on the internet or on some of the morning news shows. They are "add-on" hydrogen fuel cells that use water and your car's electrical system to boost gas mileage and reduce greenhouse emissions.

It costs $1,200, plus a few hundred more for installation.

But the manufacturer says it wouldn't take long before you made the money back.

"We estimate the average person should be able to see the savings in one year," said David Havanich, a company spokesman.

We are going to test the Hydro 4000 on a 2005 Ford Explorer. But before we do, we're going to fill the tank of this thing up and drive it around to see what kind of mileage we get without the Hydro 4000

David Havanich

So with a full tank of gas, I'm going to drive a particular route -- without the Hydro 4000. Then we'll attach the 4000 and drive the exact same route -- we'll go the same speeds, we'll drive through city and highway traffic. We'll check the mileage and compare it to when we didn't have the Hydro 4000.

We drove through South Bend and Mishawaka, but the majority of our miles were on the Indiana Toll Road.

When we were done, the trip odometer read 210.1 miles.

The Explorer had used just over 10.2 gallons.

So with my handy calculator, I figured out our miles per gallon to be 20.55.

The Hydro 4000 should be installed by a certified mechanic.

We went to Rick's Auten Road 66.

Wiring the Hydro 4000 was pretty simple, but there was a problem installing the main unit, which the manufacturer recommends be placed under the hood, near the engine.

The Hydro 4000 wouldn't fit.

Bill Rackley

"I don't think there are too many cars out there it would fit in. If they'd make it vehicle-specific, we've got some places up under the hood it would fit, but it would have to be a little different configuration," said Bill Rackley, an ASE-certified technician at Rick's.

So Bill found a spot behind the passenger-side rear tire to mount the Hydro 4000.

Because of its distance from the engine, the people who make the Hydro 4000 say our mileage may not improve as much as it could.

So how does the Hydro 4000 work?

It's filled with a combination of mineral and distilled water, and uses the vehicle's own electrical charging system to create hydrogen gas through electrolysis.

The hydrogen gas is mixed with filtered air and then sent through a hose to the engine compartment.

It is then directed to the vehicle's air intake and combined with the vehicle's ordinary fuel/air mixture that fires your engine's cylinders.

This combination creates a cleaner burning environment.

"With your computer sensors, it will change the fuel ratio that it's going to burn, because it's already got the fuel here," explained Rackley. "In theory, it should take care of a lot of your fuel consumption."

Before we tested the mileage again, we drove the Explorer with the Hydro 4000 on it for about 400 miles, and that's because the device should clean out the combustion chambers -- get all the carbon out of there. In fact, the manufacturer says the longer you drive this vehicle with the Hydro 4000 on it, the better the mileage will be down the road.

And so one more time, we drove the 210-mile predetermined course.

The gallons add up, but not quite as many as last time.

On this trip we used nine gallons; last time we burned 10.24.

Our mileage without the Hydro 4000: 20.5 miles to the gallon.

With the Hydro 4000: 23.3 miles per gallon, an improvement of nearly three miles per gallon, or 12 percent.

Assuming you drive 12,000 miles a year, you would save 70 gallons of gas.

At four dollars a gallon, you would save $280 a year.

Not exactly a mileage doubler, but the distance of the Hydro 4000 from the engine compartment likely played a role here, as did the fact we only put a few hundred miles on it.

A TV station in Florida tested the Hydro 4000 on a full size van, and after a month it went from 10 miles a gallon to over 20.

And we intend to re-test the Hydro 4000 on our Explorer in a month, to see if we also register a dramatic increase.

Our 12-percent boost did seem to prove one thing: hydrogen technology can increase gas mileage.

A big thanks go out to Bill Rackley, Rick Ferraira, and the gang at Rick's 66 for all their hard work that made this test possible.