"Miles Until Empty" unchanged when fuel added

If its anything like mine…you would have to put in at least 3 gallons of fuel before it would reset ...

 

The sensor in the tank will not register the additional gas unless you add at least three gallons.

 

i mean that your fuel gauge and miles to empty calculation will not recalculate and your fuel gauge will not show more gas in the tank…unless you put at least 3 gallons or more in the tank…at least thats what mine does…only putting in 1-2 gallons won't register on the fuel gauge and there would be no new calculations…technically you are correct…miles left = mpg x gals left…so in reality your 1.5 gallons would increase your miles left…but the car won't register it because it was less than 3 gallons…but in reality you did increase your range a bit ….

 

Interesting... I have always filled my tank up (no partials) completely and shortly after putting the car in D, the DTE would recalculate according to the new filled tank. I guess it doesn't recalculate without a full tank?

 

Even if a fill up is under 3 gallons on a Gen 2, it will not show. (I think Gen 3 is 2 gallons)

 

Your car is just fine, just fill-up when you get a chance and it will recalculate the DTE.
Enjoy your car!

 

No car that I'm aware of has a sensor that accurately measures the amount of fuel in the tank and reports it to the ECU. I doubt the Prius is any different. The sensor is in the tank to give a general idea of how much fuel remains and that is indicated by a fuel gauge to the driver. Calculations of DTE are done assuming a full and known quantity of fuel has been added to the tank.

Why would anyone bother with adding 1.5 gallons in the first place? The only time I've done that is when the only fuel available is expensive, and I want just enough to get to the cheaper fuel. When I do this, I multiply in my mind the amount of gallons I added by the MPG, and add to the existing miles remaining.

Regardless, the DTE information is always off by a wide margin, and should not be relied upon. My TSX shows 0 miles remaining when I have 100 left, or about 3 gallons.

 

The DTE is notoriously inaccurate across the entire line-up. Mine was stuck on 6 miles DTE for over 40 miles. After restarting the car the next day, it was then reading 8 miles DTE. As was stated earlier, it's just an estimate based on projected mpg. And I think it has more to do with the engineers adding some fudge factor into the programming to keep drivers from complaining they ran out of gas when the gauge was still showing miles left.

I'd be willing to bet that 65 miles showing on your gauge would have gotten you home and to the cheaper alternative with lots of room to spare.

 

trust, but verify.

 

The manual does note this behavior:

The likely reason for this is that the gauge is very inaccurate; if you get a ScanGauge or something similar, you can see the raw readout of the fuel level. It fluctuates a very large amount; easily a gallon or more, depending on whether you're accelerating/braking (the fuel is sloshing around), or if you're on a slope or not. The car gets around this by trying to average out the readings over a very long period of time. It might also take into account the fuel it knows you've consumed, for all I know. But it doesn't have a very good way of telling apart when you've added a gallon and a half compared to when the sensor reading is slightly different because you're at a different angle or the fuel is/is not moving around.

In any case, you should know that the DTE meter doesn't mean you're bone dry either; I regularly go up to 50 miles beyond the "0 mi" reading, and others experimenting here have found that the limit is in the vicinity of 100 miles (2 gallons). The manual also says that the minimum fuel required to turn off the low fuel light is 1.6 gallons, so there should be at least that much left, even according to the (certainly conservative) owners' manual, when the low fuel light turns on. That said, I wouldn't fault you for filling up anyway.

In a situation like this, where you bang up against the limitations of the instruments, you have to take into account the things you know to be true, and the limitations of the instruments; don't over-rely (or under-rely) on them. You wouldn't follow your GPS into a lake, would you?

 

I'd be willing to bet that 65 miles showing on your gauge would have gotten you home and to the cheaper alternative with lots of room to spare.[/quote]


Me too! You will learn the innuendoes of your prius if you take the time to do so, professor.

 

I think you ought to work a few shifts in the car maker equivalent of Tech Support. That may provide an 'attitude adjustment'.

Fuel tank gauging is subject to much inaccuracy (cheap components) and variability (sloshing in tank). Consumption is very highly variable with conditions (engine warmup, speed, load, traffic conditions, wind, foul road conditions, elevation change in mountains, etc.). If DTE was figured as you want, then the tank will run dry 'prematurely' nearly half the time. And such events would be very strongly biased towards the most inconvenient conditions, such as foul weather.

Are you ready to handle hundreds of thousands of angry customers who were stranded on trips where DTE said there should have been enough fuel? Even if you are ready, the manufacturers feel otherwise. Thus a huge safety margin is built into the display. This doesn't actually prevent inattentive drivers from running out of gas, but it does remove any leverage to shift blame to someone else.

As a geeky engineer myself, I would like to see the same gauging accuracy you desire, but recognize that this would open up a hornet's nest of problems.

 

So Prius has a minimum amount of fuel requirement before the gauge system resets.

The fact that it doesn't reset with "emergency" fills of less than 2-3 gallons is IMO more a testament to the having an extra gauge such as DTE and Cruising Range as opposed to poor engineering. Of course most vehicles I owned before The Prius had only the Full to Empty needle gauge. So the extra information in a Prius of a somewhat crudely estimated cruising range and DTE just seems like gravy.

I think you just have to reset your expectation not expect a reset.

I like DTE. I use it as my time to refill gauge. But it clearly isn't razor accurate. What I have found with just simple use is that especially when the tank get's low, the DTE can fluctuate, at any point less than 20 miles to empty I start to keep a close eye on it, because it can start to lose miles clearly out of sync with actual miles traveled. I've had it go from showing 9 miles remaining to Zero just driving less than a mile. Since on my Prius, once I reach Zero, I still seem to have a Gallon + of gasoline left, I don't see this as a flaw, just the reality of the gauge and sensor. In other words my expectation is not that the DTE is a perfect and exact reading, in fact since I fill up when it says Zero, I'm banking on the reality that it is NOT. If the reading was exactly accurate, I'd be in big trouble once the DTE reaches Zero, it seems to me it has clearly been designed to NOT be totally accurate and be conservative, as a safeguard against people running their Prius to empty.

It also seems to me that if you are adding as little as a gallon and 1/2 under emergency "Tide Me Over" until I can really refill it circumstance, simply knowing it takes at least 3 gallons for The Prius to reset is all you have to know.

Also it seems to me given how HSD works, expecting a DTE gauge to be entirely accurate is not sensible. Because HSD operates differently given a whole bunch of changing and sometimes unpredictable factors how can you predict how far you can go with a Prius and a gallon of gas? It depends on things as mercurial as outside temperature, and "how" you are driving the distance you want to drive. In other words DTE could calculate exactly how much gasoline is left in your tank, but it can't calculate or "predict" how you will be driving or what conditions you might be driving in over the next period. Are you going the next the 2-3 miles on mostly electric? Are you on the freeway and driving the Prius with the engine burning as much gas as possible? Is the engine warmed up and the outside temperature conducive to keeping the engine warm or is it cold outside causing the engine to turn on to stay warm more often? To expect a gauge that could know, predict and calculate all those variables to give you an exact and totally accurate DTE is IMO not a realistic expectation. By definition DTE is giving you a very crude and conservative idea of your distance to empty or cruising range, not a GTE or gallons to empty display. If it was a Gallons to Empty gauge? Then perhaps adding as little as a gallon and 1/2 of gas should be registered, but given that we are dealing with a DISTANCE to empty gauge, engineered to be conservative and keep people from running out of gas, I think the minimum 3 gallon requirement for reset is actually for most people probably a good safeguard.