Shrinking gas tank???

Yes. It happens with the Gen II Prius.

Tom

 

It's not actually shrinking. It just gets a little stiffer so doesn't get pressed into the hard tank as far from the weight of the fuel. It's a common misconception that it is -pressure- that expands it. It's actually the weight of the fuel.
"There is no pressure, grasshopper."

 

Incorrect on both counts (although the 2nd is a partial.) The bladder does shrink substantially as the weather becomes colder, up to about 15% depending on conditions. The manual even mentions this. Polymers have a larger coefficient of thermal expansion than metals, so it is more noticeable with this tank, and particularly in such a small tank.

It does get stiffer as well with the cold, but that is in addition to shrinking.

There is some vapor pressure to deal with in the tank (one of the reasons it can belch during a fill), but depending on fuel blend and ambient conditions that will differ. The system is kept at around local atmospheric pressure. However, the problem with saying there is no pressure is that the "weight of the fuel" is indeed the hydrostatic pressure of the fluid column. Pressure = F/A and P = rho * g * h. Neglecting to properly account for such pressure results in spectacular failures (see the Katrina flooding in New Orleans for an example of hydrostatic pressure undermining a poorly engineered and improperly constructed levee.)

 

Bladder shrinkage notwithstanding, the first pip will go out at varying mileage depending on how much you fuel up and the average mpg.

From a survey of my first 13 tanks of gas the first (or 10th) pip went out anywhere from 79 to 245 miles.

Does the Gen III still have a bladder?

 

No.