When is it really "empty"?

How do you know how much gas you had left? The Prius doesn't actually have a usable capacity of 11.9 gallons. If you assume that it does and try to use the mileage to out-think the gas guage, then you will likely end up hiking to a gas station when you run out of gas.

There are many, many, many posts on PriusChat from people who tried to out-think the gas guage and ran out of gas. They all follow the theme of "I've been averaging 45 miles per gallon and after driving 480 miles, I ran out of gas, even though I should have had 55 more miles to go on a 11.9 gallon tank!". They then usually admit to seeing the gas guage blinking 50 miles earlier but chose to ignore it because they knew better.

Do a search on "out of gas" for more info.

I personally fill the tank when I get down to 2 pips on the guage. That usually equals 8.5 to 9 gallons of gas.

 

<div class='quotetop'>QUOTE(N_IL_Priusfan @ May 24 2007, 10:48 AM) [snapback]449074[/snapback]</div>

I have a little, 1 gallon spare can I carry in the trunk of my NHW11, 2003 Prius. When the car runs out, I drive on to a safe area and add the extra gallon. Then I have about 70 miles to find a gasoline station. Crude, it is effective.

Bob Wilson

 

Two comments:

1) If you pump in 8 gallons and it clicks off, that does *not* mean you're now full, and there were three gallons in there. It often just means the pump clicked off before the tank is truly full. When the pump clicks off, I can easily add 1.5 more gallons every time. Additionally, capacity varies with temperature, and 11.9 is not a good constant.

2) My 2006 consistently says "Add Fuel" and starts blinking when there is 0.9 gallons of fuel left. Your results may vary, these results good for my car, my fuel gauge, and my location only.

Regards,

-Ken

 

Prius fuel tank has a flexible polymer liner. This may interfere with our efforts to get a full fuel load. Over time, my 2001 Prius has been accepting smaller fillups, even though I often drive until the "get fuel now, idiot" message is presented. Usta be 11.4 gallons, now anything over 10 is a big deal. But whaddayagonnado?

Running out is not to your advantage, so please don't do that unless you've something to prove.

 

<div class='quotetop'>QUOTE(kdmorse @ May 24 2007, 03:16 PM) [snapback]449261[/snapback]</div>

Ken's quite right. I tried the logic stated in #1 and promptly ran out of gas 45 miles after the pip started blinking and it said "Add Fuel".

I think the gauge probably works pretty well. What's inconsistent is how much gas the thing wants to accept. Now that I've had a few tanks in warm weather it seems to be getting more consistent and less fussy about filling in general (less premature shutting off of the pump, less of the car not getting along with a particular pump, and less trouble getting back to truly full). Now after a fill-up I pretty consistently get 140 miles (@46 mpg) before the gauge comes off of reading Full. This is my first summer so we'll see if that starts dropping when the weather gets cold again and the bladder starts getting stiffer.

 

Over 50F use the MFD MPG times 10, when you reach that number of miles time to refill. Under 50F use times 9, bladder shrinkage.

Wayne

 

<div class='quotetop'>QUOTE(Marlin @ May 24 2007, 12:01 PM) [snapback]449092[/snapback]</div>

This is exactly my experience. After 34 fillups, I have averaged 420 miles of driving between fillups. I have added an average of 8.7 gallons each time. Most fillups have occurred at 2 pips, maybe 5 or 6 at 1 pip, and about 3 at blinking pip.

Yesterday, I filled up at exactly 420 miles. I only put in 7.8 gallons, resulting in my best tank ever at 54 mpg.

I know I could go more miles on a tank (my personal best is 502), but why push it?

 

<div class='quotetop'>QUOTE(N_IL_Priusfan @ Jun 13 2007, 08:58 AM) [snapback]460771[/snapback]</div>

So where is the rest of the 11.9 gals if you have to fillup each time around ~8-9 gals?

Why not able to use the entire 11.9 capacity?

 

<div class='quotetop'>QUOTE(MickeyA @ Jun 13 2007, 09:29 AM) [snapback]460822[/snapback]</div>

The tank is 11.9 gallons. The bladder you pump the gas into fits inside the tank. I don't believe there is any gas tank where the usuable fuel is the entire capacity. If it didn't bother you in your last car, why does it bothe so many of us in this car?

 

<div class='quotetop'>QUOTE(wyounger @ Jun 8 2007, 07:33 PM) [snapback]458455[/snapback]</div>

I ran out of gas last week trying to push it past 500 miles. When the last pip started flashing with the "Add Fuel" warning on the MFD came on, I was only able to drive 12 miles before it ran out. It sucked because I was still 9 miles from the nearest gas station on I-5 in the middle of the San Joaquin valley in Calif. A quick call to AAA and I was moving again in 45 minutes. I was overconfident that I could travel at least 25 miles when the last pip started flashing.

I learned my lesson. When you get to 1 pip, especially when it starts flashing, BUY GAS ASAP.

Happy motoring.

 

So does the fuel gauge represent usable fuel or total fuel? i.e. is the visual gauge based on the full 11.9 gallon capacity or based on a lower usable capacity? My MFD says I'm getting 53 mpg on this tank after 270 miles, but the fuel gauge is already one pip below half.

-Sean

 

Fascinating read, only because I'm at one week of ownership, and have had only 1 fillup on the road---and that was at 2 pips left---I really wanted to go down to 1 pip (and perhaps even tempt the blinking pip) but it was the NJ Turnpike, and some of those service exits are 20+ miles apart. So, a little while after I was at 2 pips, I filled up---having done 475 miles, and I put in 9.7 gals.

So now my questions:
1. Seems clear, that the pips don't relate to gallons of tank capacity... (ie, 11.9 divided by 10 pips might suggest each pip equates to 1.19 gals.) Yet "pip #10" didn't disappear (after the fillup) for more than 100 miles (highway driving, supposedly averaging 50.1mpg.) Then, pip #9 disappeared less than 100 miles later, during the same trip. Pip 8 disappeared a little sooner (mixing in the end of that trip, with city commutes.) (Other cars were like this---you stayed on Full a long time, then the needle would seem to drop through the remaining range more consistently.) Assuming generally consistent driving over a full tank, is it reasonable to assume that the miles travelled by the time the tank gets to half-empty, would be the miles to expect, on the remaining half-tank, before seeing a blinking pip? Or is that first half of the tank not a good estimator of the remaining half, because of "staying on Full" so long?

2. Given the peculiarities described by others, in how much they can get into the tank, is it proper math to assume (from my fillup stats above) that 475 divided by 9.7 = 48.9mpg? Or, had I tried it at the pump, might I have pumped another gallon in, thus lowering my mpg to say, 44.4, had I managed 10.7 gals?! (The MFD read 50.1.)

3. When you fill up, I know the MFD resets the mileage ticker... but does it reset the Average MPG? Or does that remain "lifetime MPG" unless you manually press Reset each time?

I'm still thrilled to be so far above the 20-22mpg city average I got in my 6-cyl Accord (and about 32mpg on roadtrips)... but I'd love to know for sure that I'm squarely at 50 or better, and I'd REALLY love to see that quoted 61mpg City, after a tank of commuting... not sure that will ever happen, though.

 

It's empty when the big red triangle with the Exclamation mark in it comes on. I have put 12.4 gallons into mine without the last pip blinking. Talk about a "guess" gauge. I just make sure that my wife doesn't drive it when it is blinking, she can bring a 46mpg tank to 38mpg in about 40 miles with her right foot.

Al...

 

After learning my lesson I figure it is pushing it after topping up going more then your avg mileage X 10 after that it is pretty much time to find gas. (i am usually down to one pip at this point anyway.) Also this method makes it easy to figure out what your fillup will cost 2.70 gallon will cost $27.

 

I ran out of gas today on the freeway. For whatever reason, I did not notice the Add Fuel warning when I left this morning, but noticed the blinking gas guage halfway home. I figured I had enough to get home, as the trip is 45 miles. Two miles before my exit, the ICE shut off and I got a big red warning triangle on the dashboard. My car was now running on battery power, and quickly slowed from 70 mph to 55 mph. I had to quickly navigate onto the shoulder, where I stopped the vehicle to figure out what just happened.

I shut down the car and then restarted. The ICE was back up and running, so I re-entered the freeway and managed to go another 1.5 miles before the ICE shut down again, this time 1/2 mile form my exit. I coasted through the exit, as I had only 1 bar on my battery (used up driving 1 mile on the freeway on EV) and right into the corner gas station. Total fill-up was 12.5 gallons (it's 110 degrees outside, so the bladder must have expanded a bit).

I will from now on pay much more attention to the fuel guage, and know that there is UNDER 1 GALLON in the tank when the warning goes off.

 

My averages are: 3 bars=8.37 gl, 2 bars=9.7 gl, 1 bar=10.09 gl, flashing=11.2 gl. These averages are from 33 fuelings. I tend to "pack" the tank but not to the point that gas is in the filler neck. Three times I did put in over 11.9, 12.2 being the most (hot, 93F or so outside). Usually refuel at 2 bars and think of each bar as one gallon, even though it takes 130+ miles for the first bar to drop.

Having been a pilot for many years, fuel management is a main concern in my thinking. Why push it? The three most useless things for any aviator, all the runway behind you, all the altitude above you, and all the fuel back in the fuel pits. Have not run out--yet.