Prius Gas Gauge

Lets restate what happened for those who can not (or will not) read.

3 times I drove 20 to 70 miles on flashing fuel warning and bought less than 10 gallons. Gauge is now calibrated and behavior believed to be understood.

A few weeks later the light started flashing and ONE MILE later the ICE was dead. The gauge was taking measure of fools who trust it. Yes, the light said the engine might run as long as 70 miles based on past experience, but 1 mile isn't any warning at all. And 1 mile sometimes,

70 miles sometimes, isn't very reliable.

I continued my analysis and concluded the gauge falls about 1 to 2 gallons slower than actual (miserly) consumption. Let it sit over night and the gauge catches up. This is normal for ANY CAR, and no other car than the Prius has a bladder gas tank so its not a bladder thing.

The only thing different is that most cars use a thermistor in the gas tank for the low fuel warning light. This thermistor is very accurate, fast, and reliable. Apparently the Prius does not use a thermistor.

Why wait past 1 pip? Why wait for the flashing light at all?

Why not buy gas at 2 pips? 3? What are you trying to prove?

As unbelievable as it may sound there were no other gas stations the past 20 miles. Every one was boarded up closed. And why worry if the light is not flashing and I have always been able to drive at least 20 miles and as much as 70 on a flashing light?

The fool gauge behaves pretty much the same as any other car. "It has a bladder in the gas tank, its different!" say those who only want to be different. I find the only difference is the lack of accuracy in the low fuel warning light.

With my 2004, I have noticed that the bladder does make difference, but that difference shows when you fill the tank. We have vapor recovery gas pumps here and that seems to mean the fuel flows slower from the pump. I typically can only get 10 gallons in when nearly empty. In a neighboring county with older pumps, the fuel flows faster and I can get approx 1.5 gallons more into the tank before the nozzle shuts off. One time my wife "tried" to fill the tank at a station with extremely slow pumps. She only managed to get 7 gallons in. I think the faster the flow, the more the bladder can be expanded. That really messed with people using miles driven as an estimate of fuel left. All this is from my car only. Anyone else notice the same thing?

I always fill my 2007 on the slowest setting and get reasonable fills each time. The first bar dims between 120 and 140 miles.

Once tried to top off the tank after only 80 miles. That pump didn't want to put any gas in the tank. Later with 300+ miles on the tank the same pump pumped a reasonable fill.

6 months ago it wasn't unusual for me to bounce between 48 and 58 MPG as measured at the pump. My technique has improved since. But nothing as extreme as 7 gallons when 10 was expected.

The Prius is not fragile and the risks are managable. Running out of gas works better if you plan ahead. My fuel injectors also continue to work inspite of running out of gas.

Bob Wilson

I believe the fuel pump thing in mostly urban myth.

In the early days of electric fuel pumps some manufacturers and aftermarket installers cut corners and left the pump running all the time the ignition is turned on. When the tank is empty this can harm the pump. Modern systems only run the pump for a few seconds after the ignition is turned on, then do not run the pump until one has oil pressure or some other indication the engine is running.

your mileage can vary greatly depending on how you drove for a given tank of gas. you won't always get the same #miles on a tank or even close.

when last bar begins to blink, you have 2 galons left. when all the lights come on and you get an (!) signal in the dash, you have about 1/2gal left. don't worry about the bars til the last one blinks, then you've got about

75mi to find gas.

bob

yes, i noticed somtimes i get 520mi before the last bar blinks; sometimes i get 450mi before it blinks - both under similar driving conditions. but when i refill, the mpg seems to be the same. seems that it doesn't totally fill to same spot each time.

bob