Low Fuel Level Light - How much Left? Not much!

<div class='quotetop'>QUOTE(tekn0wledg @ Aug 16 2007, 09:51 AM) [snapback]496867[/snapback]</div>

Don't bother trying to calculate exactly how much gas is in the tank, the stock car doesn't give enough information to know for sure. The gauge is neither linear nor precise.

I often think that Toyota could have avoided a lot of confusion if they had put 4 lights instead of the digital gauge:

Light 1: Lotsa Fuel (green)
Light 2: Some Fuel (yellow)
Light 3: Low Fuel (red)
Light 4: Add Fuel NOW! (flashing extra bright with the "backup beep" and a fog horn)

 

There are actually two issues to keep in mind:

The gas gauge does not seem to be particularly accurate and its definitely not linear (each pip or bar does not represent the same amount of fuel).

The bladder in the tank makes it difficult (if not impossible) to fill the tank with the same amount of fuel each fillup. Some pumps are more sensitive and will shut off earlier than others. Even if you use the same pump every time, temperature variations will cause the bladder to expand or contract, making it virtually impossible to get the same amount every time.

My approach is to be very conservative on trying to push the limits of the range because running out of fuel is not a good thing. I don't need to get 500+ miles range; my previous vehicle could only get 240 miles max.

 

I just finished a record run(for me anyway) in my '07 Prius of 1001.6 miles and the last pip started flashing at 902.3 miles. It took 12.051 gallons to fill it clear to the top again for 83.1 mpg.

 

<div class='quotetop'>QUOTE(Sailfish11 @ Aug 16 2007, 08:09 AM) [snapback]496883[/snapback]</div>

I have run out of gas twice because I usually wait until the fuel ligt comes on. I was on the 10 in the desert during 120 degree heat wave when the fuel light came on and I literally got 2 miles! Luckily, people stopped and brought us water while we waited for AAA. I will never wait for that fuel light again! Beware!

 

<div class='quotetop'>QUOTE(melrose90 @ Oct 3 2007, 02:54 PM) [snapback]520786[/snapback]</div>

I just got a 2008 Prius. The manual says that when the light goes on, there is 3 gallons of gas left. How can that be right? Is it different on the 2008 model?

 

<div class='quotetop'>QUOTE(shoney @ Oct 3 2007, 07:45 PM) [snapback]520894[/snapback]</div>

maybe Toyota fixed the guess gauge in the 2008. Care to run out of gas to test it for us?

 

Got a little over 8000mi om my 07 that I bought in April. This last tank was the first one that I actually saw the last bar blink. Went about 10 miles to my regular gas station. I prefer to fill up when it hits one bar in town and two on the highway. Much safer that way.

 

<div class='quotetop'>QUOTE(Jim B. @ Oct 3 2007, 09:00 PM) [snapback]520966[/snapback]</div>

I use the ave mpg times 10 to estimate when to fuel up. BUT it's really important if doing this method, that the tank was filled. As others have posted at PC, you don't want to keep adding gas beyond full or you can damage the charcoal canister. But if you pump the gas fast, it may shut off too soon. And since the bladder capacity is affected by colder temperatures, the question is did you fill it within 20% of it's rated capacity? I try to pump as slow as I can without the pump clicking off. Then if the amount seems too low, I pump slowly till the next time it clicks off. That second attempt usually nets less than 0.2 Gallons. We'll have to see if my method runs afoul this winter as the bladder size changes. YMMV

 

<div class='quotetop'>QUOTE(Aces @ Oct 6 2007, 10:25 PM) [snapback]522338[/snapback]</div>

Here I am replying to my own post! Well it finally happened. I ran out of gas... sort of. Apparently I didn't get the tank full enough, and as I was on my way home from work, where I planned on refueling, about 4 miles from where my preferred gas station was, I got a series of warning lights displayed, and I noticed that my battery was showing 3 blue bars and the engine was not coming on. Fortunately, I was within 0.4 miles of a gas station; so I just drove it there! It was probably the most fun I've ever had running out of gas! It took 10.75 Gallons to fill the tank. My trip computer was saying I was getting 48.9 mpg, and I'd only driven 476 miles on that tank. In Seattle we don't get really cold Winters. And it was probably about upper 40's the previous time I'd filled-up.

So my new rule will be to multiply my mpg by 10, THEN subtract 50 miles. And while the running out of gas was uneventful; the Prius battery wouldn't go more than perhaps a mile in artificial EV mode. So it's lucky I happened to be in an urban area, yet off the freeway when it happened.

 

<div class='quotetop'>QUOTE(diamondlarry @ Aug 16 2007, 06:45 PM) [snapback]497386[/snapback]</div>

That's some impressive driving you did there. Care to give some advice? And what sort of conditions did you drive the car through to get such mileage?

 

Granted, this post won't help us understand pips and real amount of fuel left, but thought I'd relate my experience because it seemed kinda weird to me. But I bet it's within the norm of fuel gauge behavior...

The last pip started to flash to tell me I needed fuel, and I probably drove about 45 miles before getting some fuel because (a) I knew the stretch I was on had few gas stations and was not worth getting off the highway to explore to and (B) I got off the highway three times before I found a station.

When I did find a station, it was one of those places that don't have credit card readers on the pumps, and the pumps looked like surplus WWII equipment. I'm kinda goofy about this, but I tend to like to buy from stations that look well maintained, somehow thinking that the quality of their fuel may be similar. Never mind that. Anyhow, I only put $20 in the tank, which was just under 3 gallons. Figured I'd get on the road for another 20 or so miles where I knew there was a "good" station to fill up at.

So I get back in the car and start driving, but the last pip just keeps blinking. I thought it was odd that adding 3 gallons was not enough to get the "you're out of fuel" blinking pip to go away.

I did later fill up but didn't pay attention to how much I put in...I must have found the slowest filling pump on the planet and was happy to finally get back in the car and head home, uninterrupted with blinking lights, warning dings, or travels off the highway looking for gas stations.

Mike

 

<div class='quotetop'>QUOTE(SebMike @ Nov 14 2007, 11:23 AM) [snapback]539455[/snapback]</div>

Wow! $6.90 / gallon in the U.S.? I've got to remember to stay away from North Bay, CA.

<div class='quotetop'>QUOTE(SebMike @ Nov 14 2007, 11:23 AM) [snapback]539455[/snapback]</div>

Yes, this behavior is typical. It seems generally accepted here at PriusChat that you need to add just over 3 gallons for the fuel gauge to register the fact that fuel has been added.

 

With the tank full, I think, with the MPG estimate showing 54.3 MPG, actual 49.7 MPG, I can't go more than 420 miles without the one bar remaining starting to flash. This occurs on all my trips. I should be able to go approximately 550 miles before running out of fuel, but will not chance it.

Does anyone know how much the tank blatter shrinks with temp change? At what temp is the 11.8 gal figured? I know you can put more fuel into the tank at 90 degrees than you can at 25 degrees, but how much difference?

 

<div class='quotetop'>QUOTE(Tom 6850 @ Nov 15 2007, 08:18 AM) [snapback]539906[/snapback]</div>

I'm not 100% positive on this, but I believe that the 11.9 gal. stat. refers to the capacity of the metal tank. If you get 11.9 gal. or more into it, then you are probably filling up the filler tube some. The pump, gauge, bladder, and some other equipment are all inside that tank. There is also some airspace around the bladder that it is not likely to expand to fill.

I saw once a quote from what seemed like a reliable source at the time that the capacity of the bladder could fluctuate by as much as 5 liters.

 

I usually look to fill up pretty quickly after the last pip starts blinking. In my 44.5k mile fuel history, that has most often translated into a 9.0-9.5 USgal fill. Here' s a stem-and-leaf plot of my fuel fills (USgal):

4.5 7
4.8 5
5.2 9
5.3 0
5.4 8
6.2 9
6.3 5
6.7 4 9
6.8 4
6.9 4 8
7.0 7
7.1 4
7.3 5
7.4 2 9
7.5 7
7.6 1
7.7 4 7
7.8 6
8.0 0 3 3
8.2 1 6 6
8.3 1
8.4 0 1 2 6 8
8.5 5 5
8.6 0
8.7 1 1
8.8 0 1 2 3 4 5 9
8.9 3 5 6
9.0 3 3 4 5 5 6 7
9.1 0 5
9.2 2 2 3 6 6 7 8 8
9.3 2 5 6 7 9 9
9.4 1 1 3 5 5 6 7 7 8 9 9
9.5 4 7 9
9.6 1
9.7 1 1 1 2 5 9
9.8 3 6
9.9 1
10.0 8
10.1 7
10.2 0
10.4 1
10.5 7
10.6 6
10.7 7
11.7 8

(I do try to be aware of changing driving habits. E.g., first 400 miles were slow and steady 45mph returning 50+mpg, while the last 50mi were at 80mph and as low as 40mpg...)

Having said that: if my driving conditions are not severe, I usually figure I've got 30+ miles after the last pip starts blinking -- enough to drop off or pick up all the kids, which has lately been my primary metric.