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Two weeks ago I made another long trip to LA. On the return trip, strange thing happened to the data displayed in Range to Fuel when it was approaching to 96 miles left and I thought I could stop for refuel at around 30. Anyway I had to make a quick stop. At the time I got back on highway, the range was read less than 60 miles. The analog gauge also dropped further to E. This is weird - a lost of 30 miles after a stop.
Last week I did a full refuel when the range showed 16 miles left. The full refuel was 11.7 gal. I was surprised there was more than 3 gal. left with range of 16 miles. The math does not add up correctly. With 3 gal., range should show more than 80 miles or more (I expect 90 miles with my hybrid). The readout from the trip computer is not stable at least when it comes 1/4 left. The range reads over 460 miles when it is filled up in the past couple refuel. The variation of range estimation is way too off. My average fuel consumption from the Start is read 31 mpg. Anyone see such inconsistency?
 

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I haven't paid much attention to the miles-to-refuel indicator. My '16 RAV4 (non-hybrid) gas-low light comes on around 3.5 gallons left in the tank. To compare, my last two Priuses and previous Camry, the gas light came on at exactly 2 gallons remaining. Both Priuses were also suspiciously false on miles-to-refuel indicator, which read 0 with about 2.5 gallons left.

In related news: Both Priuses, a '10 and a '14, constantly showed exactly 2 MPG under what I was actually getting, almost like it was programmed to overshoot exactly 2 MPG. On the RAV4, I manually calculated the MPG estimate, and found it to be satisfactorily correct -- off by only 0.3 MPG.

I prefer to just watch my trip odometer and know about when I have to refill. The Camry, an '01, didn't read out MPG, and I got used to knowing that I would have to refuel around 400 miles. Same with the Priuses, I knew that around 400 miles I should refuel. I haven't owned my RAV4 long enough to surely know what mileage I have to refuel at.
 

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The range prediction is based on past average mpg, and it changes as you progress through the tank. So if your ave mpg is low during the first part of the tank, the system assumes that will remain true for the remainder of the tank. Its only really accurate if your MPG stays pretty constant.
 

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I ran mine down to 0km remaining and then drove an extra 20km before I refuelled, and I still was only able to get 49L in meaning there was still about 7L in the tank roughly.
 

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when it was approaching to 96 miles left and I thought I could stop for refuel at around 30. Anyway I had to make a quick stop. At the time I got back on highway, the range was read less than 60 miles.
Let's assume your fuel economy is 31 MPG on the highway. The estimated 96 miles to empty suggests that you had 3.1 gallons of fuel left. After pulling off the highway and driving through the city for a mile or so to refuel, your estimated distance dropped to 60 miles. To travel 60 miles on the 3.1 gallons of fuel, suggests a fuel economy of 19 MPG.

It doesn't seem that unreasonable that you would be getting 19 MPG in city driving, especially if you hit a few red lights, stop signs, hills, or left the engine idling while you went into a store.

A few minutes after you got back on the highway, and your speed stabilized ( i.e. fuel economy reached 31 MPG again) , you may have seen an increase in your estimated distance. However since you may have used a 1/2 gallon of gas while driving in the city, your remaining 2.6 gallons at 31 MPG would give an estimate of 78 MPG.

The readout from the trip computer is not stable at least when it comes 1/4 left.
I don't think the calculations change during the last 1/4 tank. It's just that a change of fuel economy from 31 MPG to 19 MPG makes such a change in the estimated distance that you sit up and take notice if you think you won't make it to the next station.

The range reads over 460 miles when it is filled up in the past couple refuel. The variation of range estimation is way too off. My average fuel consumption from the Start is read 31 mpg. Anyone see such inconsistency?
In cars that had warning lights for low fuel, these lights would activate when the fuel level dropped below 10%. Obviously the purpose was to alert the driver so that he would have some time to refuel before becoming stranded. My experience with several vehicles with estimated " distance to empty" calculations is that they all allow a built-in safety factor. Can you imagine all the complaints Toyota would receive if owners were constantly running out of gas,

In your case a range of 460 miles with a fuel economy of 31 MPG, indicates a fuel capacity of 14.8 gallons. That is 1.1 gallons less than your actual 15.9 gallons. In other words, you are being given a 1.1/15.9 = 6.9% safety factor. If you are the kind of person who wants to get that extra 34 miles in before refueling, you may have other things to worry about.

Also keep in mind that every car I have seen that calculates fuel economy, is always optimistic. In other words, you may not really be getting 31 MPG. Have you ever calculated your fuel economy by doing the math?.
 

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Here's a post I did in another thread back in March. I think it applies here.

Here's a quote from Autoblog: (Article - What Happens When Your Hybrid Runs Out Of Gas?)

"Here's another warning: Don’t drive your Toyota hybrid for too long on empty, or you’ll eventually need to get towed to the dealer. Toyota gave us some more information about how its hybrids function once they’ve run out of gas after we’d published this story. It turns out we were lucky we didn't deplete the battery of our Lexus HS250h any more than we did when we drove it with an empty fuel tank. All Toyota and Lexus systems are programmed to attempt to start the gasoline engine when the battery reaches its “recharge threshold.” If the engine does not start after three attempts, the system shuts down and requires a technician to reset a fault code before the vehicle can get moving again, even if fuel is added to the empty tank. There is no way for a driver to know when the battery charge gets low enough that this automatic shut-down occurs, but it’s a necessary precaution to protect the battery pack from harm."

In other words - don't run out of gas -EVER!

And, from another post:

Latest Fillup
So I let the car show me the gas light before I filled up this time to see exactly how far we could go when it comes on. It took just over 44l to fill, meaning there is ~12l left in the tank - enough to to go ~150km (94mi) before it actually runs out.
Oh, and the Nav screen shows a message saying 'Gas is low, would you like to search for nearby gas stations?' Pretty cool.
 
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Last week my low fuel light came on during my drive to work which is 36 miles from home. I dove the remaining 10 miles to work, 36 miles back home and when I finally filled up the following day only could get 12.8 gallons in my tank. FWIW my indicator showed 14 miles remaining.
 

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Discussion Starter #9
Let's assume your fuel economy is 31 MPG on the highway. The estimated 96 miles to empty suggests that you had 3.1 gallons of fuel left. After pulling off the highway and driving through the city for a mile or so to refuel, your estimated distance dropped to 60 miles. To travel 60 miles on the 3.1 gallons of fuel, suggests a fuel economy of 19 MPG.

It doesn't seem that unreasonable that you would be getting 19 MPG in city driving, especially if you hit a few red lights, stop signs, hills, or left the engine idling while you went into a store.

A few minutes after you got back on the highway, and your speed stabilized ( i.e. fuel economy reached 31 MPG again) , you may have seen an increase in your estimated distance. However since you may have used a 1/2 gallon of gas while driving in the city, your remaining 2.6 gallons at 31 MPG would give an estimate of 78 MPG.

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Very well analysis and fair consideration for Toyota. We all know each model or car brand may have its ways of preference to program or setup of its trip computer but the displaying data shall be good for general or common perception by drivers who also have variation of flavor and expectation. I was surprised for the sudden change of Range reading off by 30 miles after a quick stop (off the highway exit and straight to McDonald next to exit). I see it is difficult to accept the drop or change when driving on highway long trip where gas station could be 20 miles to 50 miles between exits. I have few other vehicles (BMW, Honda) with trip computer do not show such a big variation. I guess when I saw the big change that day with the analog fuel gauge move near E all suddenly, the first thing in my mind was I could not trust the fuel sensor to the trip gauge and computer anymore when gas station were not readily available along the highway. Actually I though the drop of fuel gauge might be caused by the pressure in the tank after a long run but it did not make sense to me how a quick stop without open gas cap would affect pressure change in gas tank or pressure balancing at a stop to induce large false reading.
I would accept a low Range number vs. actual remaining gas in the tank as long as the Range number is consistent or linear to the driving mile. Besides the hybrid has fairly constant gas consumption range. My highway range is 30.5 to 31 mpg. City range is above 33 mpg. The calculation of fuel consumption in trip computer shall be better as the range of fuel consumption between city and highway is narrow and the low side of gas mileage is constantly above 30 mpg.
Anyway, seeing these posts do help me to understand true behavior of the trip computer. Rav4 is my latest purchased vehicle comparing other vehicles I owned. I am simply expecting better accuracy of electronic devices on later model of vehicle.
 

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Besides the hybrid has fairly constant gas consumption range. My highway range is 30.5 to 31 mpg. City range is above 33 mpg.
I have personally seen the estimated DTE (distance to empty) drop suddenly, as you described, many times with different vehicles when returning to city driving after a long highway trip. The reverse is also true.

My earlier theory explains this observation perfectly, for a normal gas engine. The problem is that it doesn't explain what happened in your hybrid, considering the fact that your fuel economy actually increases in the city.

You should keep an eye on this and see if you can determine if this is consistently the case. We really don't know how Toyota determines the actual fuel used. I have suspected that it calculates the milliliters of gas used depending on the pulse width of each injector opening, similar to the way inkjet printers determine when a cartridge is empty strictly by counting the number of times the nozzle is fired. Perhaps there are other calculations being made, such as using an algorithm based on throttle position and manifold vacuum.

I still believe the method of calculation is consistent throughout the entire tank and the sudden change you witnessed was due to the change in your driving zone (highway to city) and not because your tank was in the bottom 1/4.
 

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Discussion Starter #11
You should keep an eye on this and see if you can determine if this is consistently the case. We really don't know how Toyota determines the actual fuel used. I have suspected that it calculates the milliliters of gas used depending on the pulse width of each injector opening, similar to the way inkjet printers determine when a cartridge is empty strictly by counting the number of times the nozzle is fired. Perhaps there are other calculations being made, such as using an algorithm based on throttle position and manifold vacuum.

I still believe the method of calculation is consistent throughout the entire tank and the sudden change you witnessed was due to the change in your driving zone (highway to city) and not because your tank was in the bottom 1/4.
I am pretty sure the measurement is done through gas gauge in the tank because it is a design requirement to have a gauge to check gas level in the tank. Of course, it is also easier to have a flow gauge sensor at the main fuel line to detect amount of gas actually pull out from the tank. I am pretty sure there are number of gauge sensor along the fuel line all the way to fuel injector for different purpose. But to measure Range, it would be simply get the data off from fuel tank level and divided by ave. consumption data. Fuel level read from the gauge sensor in the tank is the closest to the source with direct meaning to the data. However, how accurate of gauge for fuel level is in question. Usually the gauge do not measure the true lowest level and they are not linear unless they put more attention to custom the scale to match the shape of the tank vs. the drop height. That being all said, Range to fuel is typically inaccurate at the bottom set of fuel in the tank. I really have to run more test to see. Thanks,
 

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I rarely let my gas gauge fall below 1/8 around town or below 1/4 on long highway drives. Until the Rav4 came along, never had a miles to empty readout. I'll continue to rely on the gauge and treat the miles to empty display as entertainment.
 

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I'll continue to rely on the gauge and treat the miles to empty display as entertainment.
Or, just watch a different display. It has a purpose if you are traveling and need to know about how far you can go on this tank, but it has almost no purpose in day-to-day driving.
 

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My RAV4 doesn't have a MPG or MTE readout but my Accord does have MPG.

On a highway trip it'll read around 37. Assuming the trip has accumulated 50 miles just getting off an exit and then accelerating back up to 70 uses enough fuel at maybe 8-10 MPG to knock the average down significantly. Both the V6 RAV4 and V6 Accord accelerate effortlessly but that doesn't mean it's fuel free. If it had a MTE based on that average it would drop dramatically. If the same off-and-on was done with 200 miles on the trip the effect on average MPG would be much less.

Depending on what trip distance Toyota or other makes use to compute MTE, acceleration (or idling) would affect the readout differently. And, as Rickl showed with some figures with a low fuel tank, using just a small amount more fuel than running on the highway changes the MTE quite a bit. That same off-and-on with a full tank would change the MTE by the same number but would hardly be noticed.

So, if the OP had gotten fuel when he got of the highway instead of using a lot extra on the on-ramp his MTE would have been accurate.
 

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For reference: My 2013 RAV4 Limited showed 0 on the range as I pulled in for fuel. Put in 13.625 gallons - tank capacity is 15.9 gallons. I hope the 2.27 gallons was really what I had :)
 

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r.e. MPG accuracy. Too true! Smile.

For a new car I calculate first couple dozen tanks of gas manually to get a feel for the "optimistic" instrument reported MPG. Then I stop bothering. Can mentally adjust close enough thereafter if I wish.

So far I've only filled a new 2017 RAV4 hybrid six times with instrument vs manually calculated accuracy ranging from 97-101% of the instrument reading. Not enough data to be conclusive of course, and all fill-ups were in the winter, but so far that is better than all my previously owned vehicles! (Most have been 8-10% optimistic. Funny how that error is so consistent yet nearly always biased in one direction!)
 
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