Living Dangerously: The Fuel Light

Yup, better get AAA.

 

Sooooo many threads on this - Yes, it's an estimate, an approximation, a best guess based on many variables that the car's computer(s) has to take into account and will most likely never be an exact measure. My two cents? Don't wait for the flashing light, stop and get gas at two pips and stop worrying about it.

 

I never really used the gas estimation of the Prius. Too conservative. It goes to zero and gas tank indicator didn't peep yet. What's the use of this?
I always calculated the range I have left, based on what I actually consumed so far based on the tank (Trip A for me), for the km travelled, and then I factor in the 6% optimistic error from the MFD, and I subtract these consumed liters from the tank capacity (45L).
What is left, I calculate the range based on a conservative fuel consumption of my choice.
I made an excel table, which I printed out and keep handy in the glove compartment, to ease this calculation. I can post it again here sometime next week (don't manage before that, sorry).
I have Mpg and L/Km versions of it.

 

Has anyone gone empty yet on Gen4?
I assume it's more like Gen3 not Gen2 which ran down HV battery if you tried.

 

actually, the gen 2 had mixed experiences reported. i ran out on my '08 with no issues. (other than i had to walk home)

 

Concur.

I think people are confusing accurate with conservative. The DTE is accurate for me. It accurately tells me when I have 2 gallons left in the tank. When DTE hits zero, I'm filling up 8.5 gallons. Thus far, the accuracy is same with my Gen 2 as well.

BTW, 9.4 gallons is nothing. I've filled that much before on my PiP which has a smaller tank. Not that it's a game or anything

 

That is about what I always got with my Gen 3. However, you are the first person I've heard report that low a mpg on the Gen 4. I'm getting in the mid 60's average. I'm thinking that your lower mpg is due to the higher speeds your are traveling. I rarely go above 60 mph. I have noticed that anytime I go above 60 the gas mileage gets proportionally lower the faster I go.

 

For a variety of of technical and production reasons, it cannot be accurate. The needed measuring components must be cheap, and have production variations.

For 'customer expectation management' reasons, it must not be accurate. Most customers are not going to fully understand, let alone accurately compensate for, the many reasons why fuel consumption varies dramatically. Some safety margin ought to be built in.

The car cannot accurately forecast how future conditions will differ from past conditions. For customers who drive in variable conditions -- you have a low-MPG big highway, a better-MPG small highway, and some different-MPG city conditions -- the car simply doesn't know what is coming, so it cannot consistently mark off 1 mile of expected range per 1 mile driven and still hit '0' at the proper time. This can only work for those who drive each mile in identical conditions. Nobody does that off of test tracks

This is what we really need: someone to run the car completely out, to actual fuel starvation, under relatively controlled and consistent conditions, record progress and readings along the way, and report back to us with the details.

Bob Wilson did this for the Gen3. Someone else should do this for Gen4. Or lend a Gen4 to Bob
[WARNING] Running out of gas (Gen III) | PriusChat

 

For around $27k - I would be willing to test this out.....

 

Not yet but I did push it to its limit (or as close to it as I'm comfortable with)

Tank 2, I got 580mi and filled up at 10.828gal





One complaint though is that I think the low fuel warning light is at the worst possible place... From my eye level at my usual seating position, the steering wheel practically COMPLETELY blocks the warning light... I think they could've done a bette job by putting that on the other side of the gauge, or better yet, light up the gauge to red instead

 

I have filled mine 8 times. Each time after the DTE was --- I just like to see how far I can go...

 

And of course the 4-5% over calculation from the trip computer vs the pump/actual mpg remains consistent with everyone's observation.


iPhone ?

 

I don't recommend it, just trying to see how far we've tested the Gen4 envelope.
But I'll throw in $1 buck.

 

Neither dry, nor to the full claimed tank capacity. You clearly have NOT pushed it to its limit.

But I can accept that being as close to the limit as you are comfortable with. Hopefully, someone of Bob Wilson's persuasion (engineering curiosity, etc.) will go to the actual limit and provide a full report.

 

Well hindsight I could've probably squeezed about 620-630mi out of the tank but I wasn't gonna stretch it

 

As far as I'm concerned, if you were not planning and prepared to actually run out, carefully selecting the time and place and conditions for safety and convenience, then you were stretching it.

On the modern cars, I haven't done a first-time stretch that close to empty without bringing along a spare can of fuel. Or with a schedule to meet. Or with a passenger as a potential witness.

 

If the DTE reports the distance to x liters available in the tank, in a consistent way, then it is helpful, otherwise it doesn't help much and as I said, I never really use it. So question is, how does it calculated the DTE? based on the last tank fuel consumption, times the distance, and that is what is left in the tank after removing the liters used? Or is it using some other statistics?

Why everybody wants to run a Gen4 completely dry? to what purpose?

Unfortunately I see that the daily summary on the Gen4 does not report the average speed. A fuel consumption value without an average speed, and only a distance, does not tell much...
I am thinking I will use very few of the screens in the new Gen4 software.

 

Exactly. One of the reasons I like driving for economy is that it reduces stress (at least the way I do it!). So why manufacture stress worrying about when/if the car will run out of gas, forcing me to extricate a "dead" car from traffic? Especially in a hatchback I'm not keen on cruising around sharing the cabin with a gallon of gas in a plastic jug. "I like it here", to borrow blues pianist Pinetop Perkins' reply when he was asked how he managed to survive and continue performing past 95.

I'm not fond of gas stations, so I'm not going to fill up when the tank is 1/4 full either. With a new car, I keep an eye on how much gas I pumped when I filled the tank versus the gas gauge, DTE, blinking/ beeping refill warning, etc. Compared to the official gas tank capacity listed in the manual. My Gen 3 still had about a gallon left when the DTE was 0, but I usually refilled around that point, depending how close I was to a Shell station (which I prefer for admittedly vague reasons).

My first tank was 700.9 miles with a refill of 10.477 gallons. The gas gauge showed a tiny tad of gas left, and the DTE was around 10 miles. As I recall the manual says the tank holds >11 gallons, so that was a reasonable margin.

 

I fuel up, some time after it beeps. When it beeps usually there is about 4-6L at least of fuel, if not more, and I know that unless I am about to do a longer drive, I can drive back and forth from the office (35km total) for a couple of times, before being in the "danger zone".
There are plenty of tank stations in the city, and I usually fuel up once a month when driving only to work (one tank about 700km or so). The peep is there really just to remind me the month is over, but I never really experiment anything like going dry. I went dry once with my Polo TDI, which I was trusting because of the DTE and things like that - and I found myself stranded in the middle of the night and I was "saved" by a nice couple who drove me to a tank station to get some fuel... I dread that night, it cost me 2 hrs of wasted time and feeling quite stranded in the middle of nowhere...