When the next-generation Toyota Prius hits dealer showrooms in late May, it will come with a bigger engine, better fuel economy and solar-powered cabin cooling.
What it won't have is the innovative "fuel bladder" that has served as the Prius' gas tank since the Japanese-built hybrid first landed on these shores almost nine years ago.
Toyota decided to ditch the environmentally friendly bladder in part because some Prius owners complained that the collapsible container held much less fuel than the 11.9-gallon capacity listed in the owners' manual -- taking a big bite out of the car's range between fill-ups. In a related issue, some owners said the flexible tank's fuel gauge tended to signal prematurely that the tank was close to empty.
The new 2010 Prius -- the third generation of the groundbreaking gas-electric hybrid -- will use a rigid tank made of a lightweight resin rather than the bladder.
"The chief reason was because one of the sore points with the current-generation Prius" dealt with the fuel tank and gauge, Toyota spokesman Bill Kwong said.
The change is coming too late for Darlene Sharar, an engineering technician who lives in rural Washington and often drives in areas where gas stations are few and far between.
"In any other car I've owned, I know a tank of gas will get me 'X' number of miles," said Sharar, adding that she often could pump no more than seven gallons of gas into her 2008 Prius, even when the fuel gauge was flashing "empty."
"Instead of a range of 500 miles, I've got a range of 300 miles," she said. (The Prius gets 46 miles per gallon in combined city-highway driving, according to government figures.)
Attempts to get Toyota to resolve the issue were unsuccessful, she said. In an e-mail to Sharar, a Toyota customer service representative said the issue involved "the design of the fuel tank and there is no repair available to change the design."
Sharar eventually traded the Prius in for a new 2009 Toyota Camry.
The automaker blames the problem in part on temperature changes. The Prius owners' manual notes that the capacity of the fuel bladder drops by about 1.3 gallons at 14 degrees Fahrenheit.
As for the fuel gauge, maintenance manuals say recalibrating it can sometimes solve the problem.
Owners with a fuel-bladder problem usually complain that the tank won't take more than 9 1/2 or 10 gallons of gasoline, Kwong said.
"I've never heard of only being able to get seven gallons" into the bladder, as Sharar contends, Kwong said.
Fuel bladders, common in airplanes and racing vehicles, are a rarity in commercial passenger cars, which typically use rigid tanks made of high-density plastic, said Craig Hoff, professor of mechanical engineering at Kettering University in Flint, Mich. By collapsing as fuel is pumped to the engine, bladders help prevent fuel vapor from building up in the tank, thereby reducing hydrocarbon emissions.
The Prius' new fuel tank will use an improved vapor-recovery system that will allow the car to retain its low-emission rating from California regulators, Kwong said.