Cruising range disparity?

In order to keep customers from angrily blaming the car maker when (not if) they run out of gas (But the meter said it had enough range!), a significant portion of the fuel tank is set aside as safety margin or reserve, and not counted towards that range.

Actual fuel consumption and range is very highly variable, depending on many changing conditions that the car cannot possibly forecast, and many customers simply don't understand or cannot be expected to accurately compute. Thus, to manage customer expectations, or at least keep them from blaming Toyota when they end up running out of fuel, a couple spare gallons are set aside and not shown on the fuel gauge and distance-to-empty estimate.

My Subaru Forester takes a different approach. Its distance-to-empty gauge is actually fairly accurate. But it also has more in-your-face warnings that fuel is getting low -- a chime and TWO dashboard warning lights in bright warning colors when about 3 gallons are left, a fuel gauge whose bottom bar actually goes blank with about 2 gallons left, and a distance-to-empty display that goes blank with about 1 gallon left. And its distance gauge is always rounded to the nearest 10 miles, not 1 mile, so it is always more vague than the Prius distance display.

 

It stops at 0, at least in my Liftback. That is the very last warning. I haven't heard of other models being any different.

My 2014 Forester's DTE behaves much different than the Prius DTE. In addition to using the whole tank, the Forester forecasts based on the mpg from only the last 30-ish miles. Its estimate can climb enormously when conditions improve. I've seen it increase by more than 100 miles in the first hour after filling up, even as a couple gallons are burned off. Of course, it can also drop very rapidly when climbing into the mountains.

In contrast, the Prius DTE climbs only at fillup time. Between fillups, it never increases. Its estimate is based upon a much longer mpg history. It will also fall quickly when climbing into the mountains, though not as rapidly as the Forester. But on the downhill, it never increases. In fact, even when gliding downhill with no fuel burn at all (even regenerating and filling the battery), it still decreases at least 1 mile for every 2 miles driven. On long descents, this can cause it to reach 0 prematurely. It will also snap to 0 from somewhere around 5-ish miles remaining on flat roads, or even from 10-ish miles when climbing a hill.

For how much fuel actually remains in a Liftback, read the first post of this thread: [WARNING] Running out of gas (Gen III) | PriusChat
Your 'c' will be somewhat different, but I'm not aware than anyone has run the same detailed experiments with it.

Prior to this Forester, my previous Subaru, Honda, and last Ford all had at least 100 miles of range left when the fuel gauge reached 'E' or the low fuel warning lit up. But my first Ford was different, it actually ran dry with its fuel gauge still a bit above 'E'.

 

dye should hit zero when your last bar flashes. seems low for two bars.

 

I usually reset trip A counter, and take a picture of the Range to empty , after every fill up, to see if my C is lying to me. It usually is by 20-40 miles. It tells me range of ~ 360-380, I get around ~380-400. The pump clicks off around 8.2 ish if I fill up as soon as it beeps. Or I'll drive another 15-20 miles and hit 400 for the tank, and hope to god it doesn't run out of gas, ever again. Lucky enough, if you run out of gas, and the battery is full, it will run in EV mode for about 1.5 miles, dependent on speed and acceleration. It will get up to 42 MPH.

 

I know reading the manual is a drag, and I do not claim to have read it all. Somewhere in it is the statement that when cruising range hits 0, there is approximately 1.3 gallons in reserve. This comports with your later findings.

After you fill up, the cruising range is based largely on the mpg you got on the previous tank. I have not determined the 'formula' the computer uses to arrive at this number. I HAVE kept track, to a large extent, of the cruising range before and after filling up in my notes at fuelly.com beginning with fill-up 190 in Nov. of 2014. Before that I did keep track of cruising range after filling up beginning around fill-up 97..

If there is an interested reader with a mathematical bent who wants to tackle figuring out what the computer does, I think my information is available to the public at fuelly. The number in () is the cruising range before filling up.

 

Way I see it -- it's true: there's no time left to "cruise" -- at this point, one's neck is sore from looking for a gas station sign. Hardly cruising around. ;-)

 

This is what my manual says:

"Low fuel level warning light
Remaining fuel is low

When the remaining fuel is approximately 1.3 gal. (5.0 L,
1.1 Imp. gal.) or less, a buzzer sounds and comes on
* Refuel the vehicle."

What this tells me is that in theory, whatever the remaining cruising distance might read: at 5.0L/100K, when the buzzer sounds, I have "about" 100 km to run dry, for some value of 100 km.

 

Hi

i am new here. I have a 2015 Prius c2. I am averaging about 44 mpg. I am using Eco mode. Do you feel it is saving gas. I am only getting around 325 miles a tank full. Is that good? I'm just curious. I love the car. Most of my driving is city. Any help would be appreciated.

 

I see you have asked a few questions in various threads, and have learned, no doubt, about proper tire pressure, the size of the tank, how much fuel is still in the tank when the last bar starts blinking, ambient temperature, terrain, etc.

If you have not already watched this video, it has some good information on the basics of good prius driving. It's a regular hatchback, but the principles still apply: