Miles to Empty not accurate?

2 scenarios:

1. Consider you went on a road trip last night after you filled up. You drive the car continuously until you run out of gas. How many miles do you expect to go?

2. Consider instead you drive the car as you normally would to commute and run errands. Do you expect to get the exact same range as you did in scenario 1? Maybe, maybe not. It depends on how you will drive. The DTE only considers scenario 1 using your recent fuel economy as a basis as it can't possibly know how many times you're going to stop and shut off the car. If there is a better algorithm to use, no one has implemented it yet. Thus the DTE has earned the nickname guess-o-meter.

I find it very accurate per trip. But as an aggregate of multiple trips on a single tank, I can't rely on it.

 

Miles to Empty not accurate?
No....it's not.

My (2010) G3 reportedly has an 11.8 gallon tank.
When the DTE display goes below 20 miles remaining I get the nag beep and generally have 2 gallons left in the tank.
I'll drive a bit further and put 10 gallons in to the first click.
It's been that way for 87,000 miles.

It's like my displayed fuel efficiency.
Somewhat detached from reality.

 

No it's not accurate, and it never can be.
On my Prius I have two similar gauge readings...Miles to Empty and Cruising Range. Ones on the dash display the other on the MFD.
Both numbers are the same. Both are never pin point accurate, in fact they are conservative, and usually reach zero with at least a gallon of gas or more left.

But think about how gas consumption and a hybrid works. HSD is the synergy of two basic systems, a gasoline engine and electric motors to help increase Gas Mileage and efficiency. But since you have this synergy, and how it works depends on a lot of outside factors, such as what type of drive you are taking-short, long, city, highway, lots of hills, flat, outside temperature, engine temperature, etc...

Then how many miles you can travel in relationship to how much gasoline you have left is a mercurial reality. Unlike a regular vehicle where the engine is running constantly from the moment you turn the key to the moment you turn it off, The Prius is quite a different animal.
How far you may be able to drive on any given amount of gasoline will not be constant. Obviously you could have 1 gallon left and go upwards of 50 miles on it, assuming your engine is warmed up, and you are driving in optimal conditions for Hybrid Synergy Drive.

Conversely, you can have a gallon of gasoline left, but if the driving you are doing is uphill in the winter? Then your distance to empty or Cruising Range is going to be a whole lot less or change rapidly.

For me, cruising range or Distance to Empty is just a tool I use to estimate when I want to refill.
Warning: This is ONLY MY PERSONAL EXPERIENCE...yours may be different.
But for me, when I reach DTE=0 or Cruising Range reaches 0, I typically have over a gallon of gas left or more. The engine does NOT sputter to a stop, and I can easily continue to drive.

I don't even really pay attention to either, until I reach my final blinking Pip on the gas gauge, and then I use it to estimate when I REALLY need to fill up. And for safety and conveniences sake, I usually fill up promptly or as soon as possible, AFTER I reach zero. Paying attention to the amount to refill the tank, has consistently shown me that at least with MY Prius, I've got about a gallon or more safety margin following this protocol.

But I've NEVER expected iron clad accuracy from either Distance to Empty or Cruising Range, I view them as simply tools of estimation.

 

I pay no attention to the miles-to-empty display, never use it. I just keep an eye on the gas gauge, fill up any time it's all below half. With our low mileage that's every 3 or 4 weeks. I use the trip meter's mpg display purely for feedback, and know from experience it's over 7% optimistic.

 

After 3 fill ups since I got my 2010 Prius, I can safely say that about 9 liters of gas is left in the tank when you hit "0 miles". With my average consumption that means about 180KM to go. I always fill up when I hit "0 miles" though. The amount of gas left in the tank has been consistent.

 

Yeah, depending on your situation, but typically if you don't let it get below 2 pips remaining you'll never end up stranded.

 

mine is fairly linear with miles travelled. a drop of 26 extra miles seems a bit off to me. record every trip for the tank and post it here.

 

The DTE is even more unreliable for the PiP due to unpredictable charging opportunities.

I've never liked distance to empty displays since they cannot predict ahead of time what the driving conditions will be. I'd much rather have a display that shows how many gallons of fuel remains, and the MPG I have averaged so far. From this, and based on what I know my driving conditions will be on my current trip, I can figure my own DTE.

The miles of EV range estimate is even more problematic on the PiP, and gives people cause to complain when there is nothing wrong with their car. Something much more useful would be battery percentage, or even better, KWh remaining along with the average KWh per mile reading.

On top of all that, the DTE intentionally lies to us by a large margin. When it says 0 miles remaining, often times you can go another 100 miles. A useful DTE would have the car dying as close to 0 miles as possible.

 

Just be aware that Toyota has been very conservative with the Prius fuel gauge and MTE display. Unlike most cars, Prius owners can pretty much safely drive until the MTE says "0" and the gauge starts flashing because there is still upwards of 2 gallons of fuel in the tank. That gives the Prius an "extra" range of 50-80 miles or more. Out of 102 fill-ups, I've gone below "0" MTE several times and still have yet to add 10 gallons. When we're home, I fill up anywhere between 2 bars and "0" MTE/flashing gauge, depending on how much I expect to drive in the next few days. When we're on the road, I fill up when Gas Buddy says it's cost-effect to do so. Even my wife no longer panics when the gauge starts flashing, though she does trust that I know where the next service station is.

 

It's beyond me (being a old fart) why you would want to A. suck up all the gunk in the bottom of the tank. B. take a chance on running out of gas. C. overheat the fuel pump with is in the tank cooled by the gas. ( not sure about this on Prius) I agree with Mendel Leisk when the gauge gets down to two bars I stop and get gas. You have to stop and get gas sooner or later so why wait and take a chance. Keeping the tank full also reduces the amount of condensation you get from temp changes.

 

Any gunk on the bottom of the tank gets pulled into the fuel filter since the fuel outlet is on the bottom of the tank. The Prius cuts off the fuel before actually running out, so even if there is a fuel pump in the tank, the remaining 1/4 gallon would be plenty enough to keep it cool. In fact, fuel pumps only overheat when they run out of fuel to pump. Taking a chance at running out of fuel is minimized by knowing with high accuracy how much fuel remains and how many MPG you can expect to get with the remaining fuel.

Reasons for running a car below 2 bars of fuel remaining include;

Refueling at a cheaper station
Refueling at a more convenient station
Refueling at a more pleasant station
Reducing the number of fuel stops

I have run out of fuel only once in the Prius, and had planned ahead to reserve 8 miles of EV range for that likely outcome. I've never run out of fuel unexpectedly in any vehicle; they have all run out within a few miles of what I had estimated the range to be.

 

The main reason for running on empty is a misguided ego boost, over how far you got on a tank.

 

Agreed. Just about every car I've ever owned has behaved this way. When the fuel light comes on or blinks, I fill up two gallons less than rated capacity. 2 gallons on my 1992 Honda Accord was about 50 miles. That seems like a good margin to fill up.

My PiP at my 70 mpge is upwards of 140 miles "left" in the tank. Seems a waste of time to fill up more often with that much range capacity in the tank but perhaps 2 gallons is a good amount to lubricate the fuel pump. I fill up when Toyota tells me to. The light blinks and I get a ding which is about 10 miles DTE.

 

When I'm on the road, there's little chance of condensation building up between fuel stops. Of course, I suspect there's little chance of serious condensation here in Phoenix even when I'm home. And I doubt there'd be much difference in the amount of condensation between a tank with 2 bars left vs one with no bars given that we're talking about a total of 11.9 gallons in the first place. I don't run it down to 0 MTE unless it just happens that's where the most reasonably priced gas in the area is. We stop every 2-3 hours anyway, so I'm always using Gas Buddy to look for the most cost-effective time/place to fill up (I even preplan the night before). However, I'm not going to stop to fill up just because I'm at 2 bars if I can easily make it to a station further down the road where gas is $.20-$.50/gal cheaper. And as I said, running to "0" MTE means there's still 2 gallon left, so no danger of running out. The most I've gone past is 15 miles or so and still had over 2 gallons left. Contrast this with my van where a flashing gauge meant about 1/2 gallon left and believe me, it's a bit disconcerting when you're traveling and you put 25.5 gallons in a 26-gallon tank.

 

I consider getting fuel 100 miles after the last bar flashes and the low fuel sound is made. I've never looked at the DTE, so no idea when it says I have 0 miles remaining. Does the last bar flash when the DTE says 0 miles?

The math is extremely easy on the PiP. It has a 10.6 gallon fuel tank, which you can round down to 10 considering it cuts off fuel at 0.3 gallons remaining. Take your MPG, add a zero to the end of it (multiply MPG by the 10 gallon fuel tank), and that is very close to how many miles you can get on that tank of fuel. 51 MPG, then you can expect 510 miles of range.

I reset the A trip meter at every fill up.

 

I think it flashes when the MTE says 24-26 mi.

 

Exactly. The miles-to-empty thing is there just to confuse people---at which it succeeds admirably.

 

and if you get 65 mpg, that's 650 miles.