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I recently got a 2004 Prius, after trading in my 2003 Prius (which I only had 6 months.) In both vehicles I've noticed the following issues:

1) The fuel guage does not "go down" consistently. For instance, I recently had gone 180 miles, and it still showed a full tank. But in the next 30 miles, it went down 3 bars. Similar effects are noticed on every tankfull, mostly with the 2nd half of the bars dropping much more quickly than the first half. Can anyone explain why they do this?

2) Based on the MPG I calculate, the Prius is programmed inaccurately as to calculating MPG. MPG, specifically, is "miles per gallon", which is calculated by dividing the number of MILES you have gone by the number of GALLONS you use. (I'm a science/math teacher, can you tell?) Now, I've seen several folks post on this forum mentioning they regularly get "400" miles per tank of gas. I, myself, found the '03 Prius to vary widely - sometimes it would go 550 miles, other times only 425. On the first tankful in the newer Prius, I have gone 370 miles, and the fuel guage shows the last bar. If I extrapolate from what others have posted, as well as from my own experience, I will probably get just at 400 miles on this tankful. So, if I divide 400 miles by the 11.5 or so gallons I'll put it in when it's REALLY empty, that only gives me about 34 MPG, not the 43 that my screen is currently registering.

Has anyone else noticed this discrepancy? If so, how does Toyota manage to legally claim a higher MPG? If it's only getting 34-35 MPG, then my old Mazda 323 got better mileage...

I'm really interested in hearing responses on this, and thank you kindly for your time.
 

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I have noticed differences myself (2003/2004); personal recap:

a) On my wife's 2003, diff in display vs. actual has varied widely (wildly?) from 0.6-6.7 without any particular pattern. Actual per tank has ranged from 39.7 (my wife's first week with it after I got the 2004) to 48.2.

b) On my 2004, diff in display vs. actual has consistently gone DOWN from 5.4-0.6 across 4 tanks. Actual per tank has consistently gone UP from 38.8 to 47.0. *

c) For whatever reason, MY "first tank" on the 2003 (43.2) was higher than the "first tank" on the 2004 (38.8 ). Possibly b/c I picked up the 2003 with 81 miles on it and the hybrid battery had been fully charged in that time. My 2004 had 3 miles at pick-up (salesperson called me at work as they were bringing it off the truck), so they "only" had enough time to prep the car.

* I'll be filling up again this weekend, and I'm already at 47.5 (display); was at 47.7 @ 1682 miles this morning until the car sat in the sun at the dealer's all day and turned the interior into an oven (97F+ outside) - MPG on the way home went bye-bye in exchange for my comfort. :)

Both our cars always display higher than actual. If you want to see what people are reporting themselves, check the Green Hybrid "real hybrid mileage" database. FYI, our cars are "Hello Prius" (2003) and "Cortana" (2004). 8)

BIF, don't know how you're doing it, but you're beating me - badly; keep up the good work. :D
 

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SnakePuncess said:
I recently got a 2004 Prius, after trading in my 2003 Prius (which I only had 6 months.) In both vehicles I've noticed the following issues:

1) The fuel guage does not "go down" consistently. For instance, I recently had gone 180 miles, and it still showed a full tank. But in the next 30 miles, it went down 3 bars. Similar effects are noticed on every tankfull, mostly with the 2nd half of the bars dropping much more quickly than the first half. Can anyone explain why they do this?
I can't, but others have pondered the possible effects of the internal bladder under varying ambient temps.

2) Based on the MPG I calculate, the Prius is programmed inaccurately as to calculating MPG. MPG, specifically, is "miles per gallon", which is calculated by dividing the number of MILES you have gone by the number of GALLONS you use. (I'm a science/math teacher, can you tell?) Now, I've seen several folks post on this forum mentioning they regularly get "400" miles per tank of gas. I, myself, found the '03 Prius to vary widely - sometimes it would go 550 miles, other times only 425. On the first tankful in the newer Prius, I have gone 370 miles, and the fuel guage shows the last bar. If I extrapolate from what others have posted, as well as from my own experience, I will probably get just at 400 miles on this tankful. So, if I divide 400 miles by the 11.5 or so gallons I'll put it in when it's REALLY empty, that only gives me about 34 MPG, not the 43 that my screen is currently registering.
When your last bar blinked after only 370 miles on your first tankful, how many gallons did it take to refill? I suspect it was not 11.5.

Has anyone else noticed this discrepancy? If so, how does Toyota manage to legally claim a higher MPG? If it's only getting 34-35 MPG, then my old Mazda 323 got better mileage...

I'm really interested in hearing responses on this, and thank you kindly for your time.
I can't speak for anyone else, but I regularly meet or exceed the 400 mile mark with every tankful and have yet to add more than 9 gallons at fill-up. In other words, the last bar on your fuel gauge may start blinking at approximately 400 miles, but it is unlikely that your tank will actually be empty.

Drive happy,
Moo :)
 

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SnakePuncess said:
...The fuel guage does not "go down" consistently. For instance, I recently had gone 180 miles, and it still showed a full tank. But in the next 30 miles, it went down 3 bars. Similar effects are noticed on every tankfull, mostly with the 2nd half of the bars dropping much more quickly than the first half. Can anyone explain why they do this?
Most of my cars had guages that dropped faster during the 2nd half of the tank. Particularly guilty of this was my BMW Z3, and my 1999 Corvette.

My non-engineer guess is that it could have to do with the float-mechanism inside the tank, and the arc at which it travels.

I can't explain a 3-bar drop in 30 miles, though. My Prius II doesn't do this. It drops from top after about 150 to 160 miles, then after that, it drops a bar approximately every 40 to 60 miles, depending on my driving patterns, road conditions, etcetera.

I try to fill up whenever I reach 2-bars left.
 

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BIF said:
My non-engineer guess is that it could have to do with the float-mechanism inside the tank, and the arc at which it travels.

I can't explain a 3-bar drop in 30 miles, though. My Prius II doesn't do this. It drops from top after about 150 to 160 miles, then after that, it drops a bar approximately every 40 to 60 miles, depending on my driving patterns, road conditions, etcetera.

I try to fill up whenever I reach 2-bars left.
Engineer's response:

Your first comment is partially correct. The arc of the level sensor is part of the issue. The other issue is every auto manufacture that I have knowledge of establishes a full point such that a mostly full tank will indicate full. This is done to address the pumps that will not fully fill the tank, including those with vapor recovery, and other reasons why the tank will not fully fill, such as filling at a station that is on an incline. Simply a customer satisfaction issue (hey, I filled my tank but it doesn't show full). This results in a significant non-linearity during the first 2 - 3 gallons used in most vehicles.

The second issue is the result of the algorithm that reads the fuel level signal and digitally filters it. This is a complex algorithm that differs with each manufacturer and attempts to address fuel level changes that result from slosh, road vibration, and inclination changes. Some are good, some not so good. The Prius uses a 2 float mechanism that is supposed to allow for more accurate readings of fuel level when on a non-flat surface. While I have had no issues thus far, many others have reported significant non-linearity at certain times, indicating the filtering algorithm is reacting to some sort of level change that indicates it should update the level displayed due to a current inaccuracy. What this demonstrates to me is that Toyota needs to continue to work on their fuel level algorithm, as it clearly can be improved.
 

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Discussion Starter #6
OK, just put in my 2nd tankful....

OK, this 2nd tankful got 480 miles before the light began blinking. I put in 11.2 gallons this time - so I didn't have much left!! Last time, it blinked with 2.9 gallons remaining. This is a huge difference, and one that is rather disconcerting. To know that I can't count on my fuel gauge to be correct is very, very bad. I've always been able to judge when previous cars were 1/2 full, etc., even when their gauge was somewhat off, because they were consistently off the same amount. With this car, it's so inconsistent that I can't even begin to guess!

Oh, and I *HATE* that it resets itself with every tankful. The '03 Prius didn't do that, and I'd prefer this one not to, either.

::::grumbling::::

I still love this car, but this is a definite downside that I'm not happy about....
 

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Re: OK, just put in my 2nd tankful....

SnakePuncess said:
Oh, and I *HATE* that it resets itself with every tankful.
It does? Pardon a dumb question, but at what point does the reset take place? Every time I fill up, I get back in the car, turn everything on (without starting it), write down (and manually reset) the trip odometers, and then write down the MFD values and press reset before I actually start the car. Maybe I'm missing out on this "feature"... :wink:
 

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Re: OK, just put in my 2nd tankful....

TechnoMage said:
SnakePuncess said:
Oh, and I *HATE* that it resets itself with every tankful.
It does? Pardon a dumb question, but at what point does the reset take place? Every time I fill up, I get back in the car, turn everything on (without starting it), write down (and manually reset) the trip odometers, and then write down the MFD values and press reset before I actually start the car. Maybe I'm missing out on this "feature"... :wink:
The MFD resets after each fillup before you even drive a tenth or two of a mile. I think it purposely doesn't reset until you begin driving, just in case you have turned the car on while you fill out your mileage log (like I do).

TRIP A and TRIP B only reset when you manually do it.
 

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TechnoMage said:
FYI, our cars are "Hello Prius" (2003) and "Cortana" (2004). 8)
Okay, I've never really understood the whole naming of cars, but damn, Cortana is a great name for the Prius! (see avatar) She's guiding you, giving you waypoints, and the fuel gauge is like a healthbar. I especially like how the bars appear one at a time when you refuel.
 

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After I watched the CBS special a few weeks ago when they picked apart the milage claims of the Hybrids I got an unreturnable message off to cbs news. They used several exotic fuel flow meters etc: for the tests which they failed to use on any of the SUV's included in test. They never got better than 39 MPG. I asked the question "What ever happened to filling up tank and driving three hundred miles and then filling up at same pump and using the calculator. I've done this four times in the past 2300 miles of driving and have never seen less than 49 MPG.
 

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Re: OK, just put in my 2nd tankful....

SnakePuncess said:
OK, this 2nd tankful got 480 miles before the light began blinking. I put in 11.2 gallons this time - so I didn't have much left!! Last time, it blinked with 2.9 gallons remaining. This is a huge difference, and one that is rather disconcerting. To know that I can't count on my fuel gauge to be correct is very, very bad. I've always been able to judge when previous cars were 1/2 full, etc., even when their gauge was somewhat off, because they were consistently off the same amount. With this car, it's so inconsistent that I can't even begin to guess!
This is interesting. My last tankful went 397 miles before the last fuel bar began to blink and took 8.1 gallons to fill up, which is pretty standard for me. You went 480 miles on 11.2 gallons. Assuming your consumption screen indicated approximately 43 mpg, then you could use math to avoid running out of gas. However, IMO, you should still take it to your dealer and have them try to re-calibrate the gauge for you.
Drive happy,
Moo :)
 

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Richard said:
Okay, I've never really understood the whole naming of cars, but damn, Cortana is a great name for the Prius! (see avatar) She's guiding you, giving you waypoints, and the fuel gauge is like a healthbar. I especially like how the bars appear one at a time when you refuel.
Look closely at the pic on this page; gotta love Photoshop. :) Haven't yet done a modified interior shot of the MFD but,... let's not give away the idea just yet... ;)

"Betcha can't stick it..."
 

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My latest tank was 157 miles and 2.4 gallons. That's 64.4 MPG by way of calculator. I don't think Toyota needs to explain or apologize for anything when I'm getting nearly 10 MPGs better than the overall EPA figures...

Anyhow, my numbers are in the mileage database over at http://www.greenhybrid.com.
 

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Re: Fuel gauge inconsistencies

I have a new 2004 Prius and I have also experienced lower than advertised fuel mileage and confusing fuel gauge responses. I try in both the city of Chicago and on major highways all over. On my first tank of gas the fuel gauge did indeed drop down inconsistently. When the last bar was left I decided to fill up and I the pump put in 9.5 gallons before the pump clicked off. I had only driven 350 miles at that point so if you do the math that is a MPG of only around 36 MPG. I am a very consistent driver who does not accelerate rapidly, I coast at times to conserve gas, etc. 36 MPG is crap if you ask me, especially with an EPA 50/61. Anyways, maybe things will improve. Finally, with my second tank of gas I drove slightly over 100 miles before the first bar dropped off the gauge. Then, over the next 100 miles the tank is now half empty according to the gauge. Why can't little nerdy scientists design a more reliable gauge? That's pretty messed up if you ask me. :(
 

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For me, 3 going to 2 bubbles on the level indicator takes 8-8.5 gallons (US) before the pump clicks off. Same pump all the time too.

Current lifetime (04) actual MPG is 46 +/- 0.5. It actually agrees quite well with the MFD display.

I generally refill at around 400 miles (indicated on the MFD), but have hit 500 without the last bubble starting to blink.

Habits: Primarily Highway (80%), speeds generally 65-75.
 
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