Last Bar

No. I'd keep doing what you're doing.

How much you get on the last pip can vary a lot, depending on the car and the guess gauge's calibration. How many gallons in a reserve tank when the last pip start blinking? | PriusChat is an example of such discussion and data points.

The Gas Gauge Says Full, But That's Not Quite True: NPR | PriusChat should give you some perspective, even though it's a Ford engineer talking.

Just because the tank has a rated capacity of 11.9 gallons doesn't mean that there are 11.9 gallons in there and that all of the fuel in there is usable. To make matters worse, there's the capacity variation of the bladder.

 

If you want to push farther on a tank, consider first getting a newer model without a fuel bladder. While our Gen3 fuel gauges are no better than any normal old nonhybrid, i.e. not nearly as precise or accurate as many drivers wish, at least they don't have the huge added uncertainty of the Gen2 fuel bladder. I remember more than one Gen2 driver running dry with the 'guess gauge' still at 2 bars.

 

Why are so many people intent on squeezing the last drop of fuel from their gas tank? You're flirting with disaster (well, maybe just a major inconvenience.) If you get down to one bar, fill it up. If the last bar is flashing, fill it up quicker.

 

Some people climb mountains to get their adrenaline pumping.

Others jump out of planes.

Here at Prius Chat we meet those radical dare-devils who...

...like to drive with very little fuel.

 

Where I travel, waiting for the last bar is too late to start fuel planning. This isn't the longest no-services segment seen this year, merely the only one for which I grabbed a picture:



This subject gives me mixed feelings. On one hand, there is normally little excuse for accidentally running out of fuel.

But on the other, there have been multiple scenarios in the past when one had very good reason to travel a long distance (compared to the available car's fuel range), under circumstances (location, time/holiday, weather emergency, or geopolitical crisis) where fuel was either unavailable, or subject to serious price gouging. Does anyone remember the news stories of 1970s gas shortages, with alternate day fuel rationing in some states, where some familes had to travel on a specific day when they couldn't legally buy fuel? Or hurricane evacuations where the gas stations ran out, or were de-staffed before the main evacuation started? Or widespread power failures that shut down all the fuel pumps? Is anyone confident that none of these could ever repeat?

I've described the long distance weekend holiday price gouging incident that forever altered my fuel planning, in past posts.

Other discussion suggested that most pilots know their craft's fuel range to about ten minutes. Why should we tolerate the two hour gauging uncertainty of typical automobiles when there are a few situations where much greater accuracy has great value? I believe in refining the bottom-of-tank estimate under benign conditions, before a real high value need arises. Because of the uncertainties, some folks will run dry will making these tests. As long as they are prepared for the consequences and don't create a hazard to others, we shouldn't give them undue grief for trying.

 

I'm not trying to give anyone grief. If someone wants to push the envelope, have at it. For myself, there are situations where I like to stay within my comfort zone. Not running out of gas is one of them. Since I live and work in a metropolitan area, finding a gas station is not an issue, but that's still not reason enough for me to chance getting stranded. To each his (or her) own...

 

Pilots carry less than a full tank of fuel to fly more efficiently. They've a reason to plan down to 10 minute resolution. Most folks don't do that with cars.

Besides, our cars don't drop out of the sky if they run out of fuel.

If we know our cars to be unreliable at measuring fuel, plan accordingly... carry a spare fuel can when driving in BFE. It's that simple.

 

While I agree that one should plan to never run out of gas, I wonder why we countenance the absurd lack of accuracy of automotive gauges. Time and frequency can be measured to parts in 10^15, most physical quantities can be measured to tiny fractions of a per cent accuracy and even better resolution. Why do we put up with gas gauges that can be off by 10%, gas consumption "measurements" that are routinely off by 2%, speedometers that always read high, and the idiotic "TPMS" (tire pressure "measurement" system) whose readings are either "OK" or "LOW" when the actual tire pressure can easily and valuably be displayed.

And, since I'm being cranky, what's with the "codes" that you have to root around for when something goes wrong with a vehicle? Why not display the actual defect on the car's display? Grrrrr.

For a few extra bucks we could have accurate gas gauges instead of a terminal blinking bar.

Richard

 

what choice do we have? who is going to buy a car because it has an accurate gauge? and is anyone actually testing to see which is most accurate?

 

All the more reason to not hassle automobile operators for operating as close to the fuel margin as do aircraft operators.

Only 10% ? I'd be very happy to have a fuel gauge that accurate!

Except for that long-ago car that ran dry with the needle still above E, all my cars (of four different brands) have had 20 to 35% more range available after reaching nominal gauge 'empty'. (The 35%-er is still in the household.) 10% accuracy is about where I'd quit pushing the envelope.

 

I'll stick with Lord Kelvin on this one. I don't want my car falling out of the sky.

Richard

"When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge of it is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced it to the stage of science. "
Sir William Thompson, Lord Kelvin (1824-1907)

 

When you drive on 1 bar for awhile, that single bar starts to flash and you get a "LOW FUEL WARNING" on the MFD.

 

Wife tried to push it 3 weeks ago.. got the bar symbol and went for 50 miles beyond the "Low Fuel Warning"

She got about 10 more miles and then the car started to SLOWOWWW down.

Then it happened.. the christmas tree lights came on the dash.( I do not know which ones, I wasn't with her.)
Car died.. she at least got it over on the shoulder of the free way.

Luckily, her cell phone died.. but her friend called up the Auto service and paid them the $5 for the gallon to get home.

 

I have never pushed it that far! When you put the 1 gal of fuel in the tank, was the engine hard to restart?

 

Similarly ... just a week ago, I had to travel about 140 miles to-and-from the Indy Airport. I had four or five "pips" while heading out of Lafayette and MIGHT have been able to make the entire trip without needing gas, but I went ahead and filled it up.

It was about 40 miles from home on the return trip that traffic on I-65 came to a halt; it took about 35 minutes to cover no more than 2 miles! It was about 10:30 pm but STILL nearly 90-degrees / quite humid / little-if-any wind. If I hadn't filled up, I probably would have been on my last "pip" by then AND going nowhere fast AND having to run the A/C; I'm not going to subject my wife / daughter to no A/C in those circumstances.

In short: one NEVER knows when an unexpected situation / emergency might arise - that's why they're called UN-expected - and that's why I always fill-up no later than VERY shortly after the 3rd pip goes out.