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I have a new 2005 Prius Package 4. I was wondering if anyone has wathced their fuel gauge and noticed that at 1/2 tank it only takes 4 gallons or so to top off? I also ran it down to only two bars left on the fuel gauge and it on ly required 5.9 gallons to top off, it seems I should at that point be reading around 1/2 tank should I not?? Please let me know if anyone else has noticed this. I may need to see the dealer.

Driftwood1
 

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Fuel gauge

Welcome to the crazy world of Prius fuel level guess gauge.

When checking for posts, for this item you will find many have posted something about how crazy this one item works.

The best thing I've seen for this is two simple points.

Drive until you have one square left, then refuel.

Take the MPG on your MFD times 9 and use it for your total miles for that tank of gas.

Now relax and enjoy driving and smile at all the SUVs and pickup trucks you see on the road. Because this summers high gas prices are just a look ahead to what will be the norm.
 

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It's not a linear guage, but neither are most analog guages. My own personal strategy is to drive until I'm down to one pip onn the gauge and then fill. This is usually around 400 miles driven and I usually put in about 8 gallons. It is hard to get a consistent fill because of the fuel tank bladder which is designed to reduce the environmental impact (when I realized this, I stopped trying to "burb" the tank to get more gas in).

Note that the Prius is the only car in which people seem to routinely run out of gas. Because the guage is so obviously nonlinear, people try to "game" it to get the most miles between fillups. I'd just as soon fill up more frequently and never run out of gas...YMMV, literally.
 

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At 400 miles, I have close to another 200 miles before needing fuel.
Yo DanMan, it's time for you to take astrowomans advice and start thinking about gas. If you will just start noting your odometer info we'll continue with the advise about filling the tank!
Don't want you having to sit in anymore intersections. One extra visit to a gas station a month won't cost you one dime more.
 

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When I'm down to two or three I start looking for the lowest prices. If I see a really good price (relativly speaking) at three and have some extra time, I fill then, usually about 450 miles on the tank, when it's at two, I fill at the next convienent stop with an acceptable price, about 500 miles then. If I let it get to one blip, first station I come to.
 

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hyperion said:
DanMan32 said:
At 400 miles, I have close to another 200 miles before needing fuel.
Yo DanMan, it's time for you to take astrowomans advice and start thinking about gas. If you will just start noting your odometer info we'll continue with the advise about filling the tank!
Don't want you having to sit in anymore intersections. One extra visit to a gas station a month won't cost you one dime more.
Thanks Hyp. For one thing, I don't get to one pip until about 500-550 miles, which means I have about 40 miles before it goes blinking, and at LEAST 50 miles after that. I don't go too far on blink though, strategizing when and where I fill within my commute.

I usually fill just a bit more often than once a week. I couldn't make it waiting a month to fill up.
 

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Here is a thought -- we all get used to the behavior of the car under our normal driving conditions. For me, that's a 15-mile commmute on freeway amongst rather agressive fast drivers in fairly heavy to very heavy trafic with some rolling and a dominant grade -- For Dan it's flat and relatively mellow (I just spent 3 weeks in FL with a fair amount of miles on US 19) and where there are lights they are LONG compared to here.

If you do the same thing reproducibly, the car will behave fairly consistently modulo the weather and any variations in the shut-off sensitivity of the pump you last used to fill. HOWEVER, when you take your car on a road trip under different conditions, you may suddenly find you get considerably different and more widely varying mileage. My personal recommendation is to pay attention to all the indicators and don't get too attached to going a certain number of miles before filling without factoring in changes in driving conditions -- that's the way people run out of gas in this car. I've even read reports here of the car actually running out quite soon after the last pip starts blinking, so I don't wait that long.
 

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driftwood1 said:
I have a new 2005 Prius Package 4. I was wondering if anyone has wathced their fuel gauge and noticed that at 1/2 tank it only takes 4 gallons or so to top off? I also ran it down to only two bars left on the fuel gauge and it on ly required 5.9 gallons to top off, it seems I should at that point be reading around 1/2 tank should I not?? Please let me know if anyone else has noticed this. I may need to see the dealer.

Driftwood1
Your guage is fine. It is behaving the same as all of ours. Enjoy the car and fill up when it convenient, or when you get to the last pip.
 

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Just recently I came to understand the fuel guage.

It works just like the SOC indicator on the MFD.

When it reads full, it's really only 80% full.
When it reads empty, it's really only 80% empty.
 

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The Toyota engineers went a bit too "safe" on the programming side for the gasgauge ( yes, guess-gauge ). I found, that the bladder sensor reports 0-empty value, sometimes when even there are more than 3 gallons ( ~11 liter ) is still in the bladder. It is without a question a hard task, nevertheless, they should've been able to solve it...

I don't envy the engineer who had to write the software for the gauge, again, the sensor readings are quite eratic... They should've taken into consideration the accumulative MPG to "sanity-check" the sensor values...

Check out my measurements :

http://www.vassfamily.net/ToyotaPrius/C ... index.html


Cheers,
Attila
 

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Ah, but you started by assuming that the bladder was completely filled. There's no easy way to verify that assumption.

I'll bet attila a dollar that he can't drive 80 miles after the last pip starts blinking. (But not you, Dan; anyone who gets 600 miles per tank has some special mojo workin'.)
 

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I've driven 82, or maybe it was 87, I can't remember. The way my guage has been reading lately, I believe the flashing pip is triggering earlier than it used to, so I believe I could go 100 miles. But I don't want to try it without being within 2 miles of a gas station at any time, or extra gas in a can.

Even with such erratic readings, they could smooth out the readings.
 

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richard schumacher said:
Ah, but you started by assuming that the bladder was completely filled. There's no easy way to verify that assumption.

I'll bet you a dollar that you can't drive 80 miles after the last pip starts blinking.
You are right, I chicken'd out at around 70 miles, since the next morning I had to take my daughter to the DayCare and imagine what my wife's reaction would've been if I said "Sorry Honey, I wanted to check the size of the bladder..." whaaaam! No Dinner! But seriously, I always drive at least 40~50 miles without even starting to look for a gas station after the blinking starts. In my usual drive, I have stations at about every mile or two, and I know that EV would take me there if need be...

Attila

Btw, if you raise your bet, I'll try it! :twisted:
 

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Fuel Gage and Fill Considerations

I finally got around to poking through Toyota's TechInfo Web site today and found some interesting info about the Prius Fuel Gage and Tank/Bladder system: (Section 4 of Prius Technical Training document "Engine"):

Regarding Fuel Gage Inaccuracy and Filling Problems:
1. The fuel level sensor is direct-acting and involves a magnetic float which rides in a tube with a surrounding coil. A Level ECU then measures the slight difference in coil potiential.
2. There are also two sensors that sense side-to-side and front-to-back vechicle level and are used in calculating/adjusting Fuel Level. There is also a Temp Sensor in the tank.
3. There is supposed to be virtually no Vapor/Air space in the Fuel Bladder. The Bladder Expands and Contracts with changes in Fuel Fill and Fuel Temperature.
4. The Bladder cannot expand as much at lower temperatures. At 14F the tank capacity is reduced by more than a gallon.
5. The document states that filling the tank with the vehicle on an incline might result in the vehicle runnning out of gas with 3-4 Bars Left if the incline sensors are out of calibration.
6. Filling the tank REQUIRES that the GasPump nozzle seals into the rubber seal of the filler neck in order to inflate the bladder during fueling. Cycling the nozzle in&out while filling or having a poor seal due to nozzle damage will reduce the amount fuel accepted by the bladder.
I presume that this means that air has bled into the bladder ... burping the bladder at the end of the fill by cycling the nozzle slowly in&out, adding more fuel, etc. seems to purge the excess air and allows one to add as much as 1 gallon of fuel.
7. There is a NOTE that overfilling may cause EVAP system problems (fuel pushed into EVAP System)
8. They also note that the HV ECU tracks many pieces of data over 3-6 weeks of driving to refine MPG calculations (Driving patterns, mph, load, etc.)

So, this helps to explain many of the Fuel Gage and Fuel Fill inaccuracies and idiosyncracies.

My Fuelish Rules:
1. Fill tank on a level spot!
2. Inspect Pump Nozzle for scratches, dents and dings. Try to use a one in good condition.
3. Take you time in filling the tank. Slow filling seems to help in ensuring a full fill.
4. Try not to fill the tank in frigid weather (fill the tank right after leaving a heated garage).

Hope you've had your fill on this topic because my bladder is full!
 

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A lot of good info but regarding your fuelish figures
1. I believe it is required that all areas around fuel pumps be relatively level. (can't remember ever finding otherwise)
2. Much easier to observe in Austin Tx but in New England with the temp in the twenties and the wind at 35 mph, ears freeze up quickly and fall off, so you pump as fast as she goes and take any condition nozzel you find.
3&4. After leaving that heated garage and driving several blocks you can forget the warm bladder including the one in the tank.
As for guage reliability, forget it and plan on gas no later than when you observe 350 miles on the odometer. (ears and all)
 

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Fuel Fill on the level

Regarding Gas Stations with non-level pavement at the pumps:

Actually, one of my early Prius Fuel Fill glitches occurred at a Gas Station in Austin where the pump islands had a slope in both directions. When I pulled into the island my prius was tilted both left-to-right and front-to-back.
 

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Lots of stations around here have slopes near the pump.

Can you site location of your info? Granted, I didn't take very detailed look at the fuel system, but I never read information as specific as yours, though there was enough information from calibration information and diagrams. My info is from 2004 info though.
 
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