Reading the reams of coverage pouring out on the 2010 Toyota Prius, we realized we hadn't covered one new feature that corrects an irritating problem with its predecessor, the 2004-2009 Prius hybrid.

That was the earlier car's fuel "bladder" gas tank, a flexible membrane that expanded and contracted as the volume of gasoline changed. It was contained inside a metal shell for rigidity and protection from road hazards, so many owners never knew it was there.

The new 2010 Prius uses a conventional, rigid tank, albeit one made of lightweight reinforced resin rather than steel.

The notion behind the bladder was to control evaporative emissions of gasoline fumes. In the old design, rather than replacing the gasoline consumed with an equivalent volume of air, the bladder would shrink around the fuel.

But as Toyota Prius owners in cold climates learned, the bladder also shrank in winter weather. And the loss was substantial: Even the owner's manual warned that tank capacity could fall by as much as 1.3 gallons at 14 degrees F (-10 degrees C).

That's more than 10 percent of the tank's stated 11.9-gallon capacity. Some owners complained the hit was worse, saying they could only get 9 gallons--sometimes even less--into their tanks, severely hurting the car's theoretical 500-mile range.

Toyota Prius gas cap

Toyota Prius gas cap

In switching to a standard rigid tank, Toyota added a conventional vapor-recovery system. That new hardware lets the 2010 Toyota Prius keep its rating as a low-emission vehicle under the state of California's stringent standards for volatile hydrocarbon fumes.

For a complete dissection of the gas tank and bladder from a 2004-2009 Prius, see the excellent step-by-step photography on PriusChat, from which we have taken the liberty of borrowing the image below.

But one final question: As we bid adieu to the bladder, should we be humming "Tanks for the memories"?

Toyota Prius gas tank bladder, from PriusChat user galaxee

Toyota Prius gas tank bladder, from PriusChat user galaxee

[Chicago Tribune via Autoblog Green via TreeHugger]