Low on fuel coming on too early?

My Gen2 cars are all different, one will get me 320 miles and my own fuel light will turn on, while another will get me 370 miles before that light turns on. So you really have to gauge the car you own to see exactly where you stand when that light turns on. On the 320 mile fill ups, it'll normally be under 8 gallons, however the 370 miles fill ups are usually over 9 gallons. Gas stations are all over the place here, so I just fill up when the light is on (and often even before that)

 

Gen2 tanks have a flexible bladder in the tank that actually holds the gas. It causes the "reserve" to fluctuate and has been an issue since day one. Gen3 and beyond did away with the bladder because one time you might get 75 miles after the low fuel light, the next time it could be twenty miles. So fill up immediately on low fuel or even sooner.

 

As others have mentioned, Gen2 Prius in the US have a "flexible" bladder inside the gas tank that actually contains the fuel. The idea is that the bladder "inflates" when you fill it and "deflates" as it empties. Think of it as a water ballon- but much less soft and squishy.

Toyota wanted the fuel inside to be stored without the "airspace" above it that a normal gas tank has- that space lets the liquid slosh around and creates lots of gasoline vapors. (vapors are "hard" to deal with on a hybrid)

The bladder design minimizes vapors but the bladder gets less flexible as it gets older, more so in cold weather. So the useable capacity of the tank is reduced. Also a normal fuel gauge setup won't work in the bladder so we have an inaccurate "guess gauge".

It's no wonder that Toyota dropped the design when they released the Gen3. For comparison I fill my 2006 when the gauge drops to 1 bar and usually get 7 gallons.

Posted via the PriusChat mobile app.

 

I've had a 2008 about 12 years and the fuel guage has always been irritating. Suddenly the low fuel warning light blinks constantly and doesn't go off when the tank is filled. I normally rely on the trip odometer and refill after about 350 miles but my senior citizen may not be doing as well as she did when she was young. Is anyone familiar with this problem.

 

Hello and welcome to Prius Chat!

Looking at your description, my first guess is that the sensor inside the fuel tank (that measures the fuel level) is worn out and failed. Seen that a few times on the Gen2 Prius.

Unfortunately on this design, the fuel tank is a "sealed" unit, and in order to replace anything inside it (like the level sensor or the pump) you have to replace the entire tank assembly.

Before doing that you should have that guess confirmed by testing the resistance of the level sensor (aka the gas gauge sending unit). The connector is accessed by removing the rear seat bottom cushion and prying up the metal plate on the left side.

The service manual has the wiring details, but the sender should be between 4-110 ohms resistance. When they go bad it will read a couple hundred ohms or just open circuit.

Posted via the PriusChat mobile app.