More Perspectives on the Elusive Fuel Gauge Accuracy...

[Mystery Squid]

...last square started blinking at around 480 miles. Went to fill up, managed to get 9.4 gallons in, which is an average of about 51 m.p.g., which concurs with the computer...

I have an '04, no work done with respect to the TSB pinned above, weather has been 60's-70's fahrenheit. Seems reasonable to me... Given, unless anything changes, I really don't think I'll make the time, nor undertake the effort, to get it "fixed"...

[Tideland Prius]

Mine started blinking at 794kms, I pumped at 818kms. Farthest distance (so far) that I've dared travelling on a blinking light

[moshe1436]

I just completed a trip from Florida to New York and averaged 50.2 mpg overall with a loaded vehicle. On one leg of the trip I was approaching 450 miles on a tank of gas but the gas gauge still had 4 pips on it! I was panicky but made it to a station and put in only 8.3 gals. The MPG for that leg was 50.3. I seriously question the accuracy of the gauge and probably will never trust it again. Anyone else with this experience?

[Neicy]

Originally Posted by moshe1436

... I was approaching 450 miles on a tank of gas but the gas gauge still had 4 pips on it! I was panicky but made it to a station and put in only 8.3 gals. ....I seriously question the accuracy of the gauge and probably will never trust it again. Anyone else with this experience?

As I posted in another thread, my last tank was 485 miles, went from 2 to 1 PIP at 431 miles, and as I sat waiting for my usual pump it beeped and then started flashing. It clicked off at 8.73 gallons. Go figure.

[kfs2840]

I refuel based on miles since last fill, not gauge reading

[richard schumacher]

Originally Posted by kfs2840

I refuel based on miles since last fill, not gauge reading

After how many miles? If it's 200 you should be fine. If it's 500 you will eventually run out.

Pretty much the only way the gauge can be inaccurate about running out is if the last fillup occurred on a sharp slope, which can throw off the tank's tilt compensation.

[ZC1]

Speaking of fuel gauge readings,

from a FULL tank (according to the pip meter), knock off TWO complete pips and what do you get?
77miles.

What does the MFD say?
61 miles of the 77mileage is at 55mpg.

Huh, Eeekk, What to do ...What to do?

Actually, I'm going to report this to my nearest:
No one.

One month and one week old 2008 car with only 384(?) mileage and a hardly used fuel bladder, what else should I expect?

Fortunately, I have fuel bladder experience in helicopters I flew both in icy weather and in very warm weather (read: Iraq).
A helicopter pilot performs an ongoing fuel check/calculation during flight to check fuel drain, never depending his life on a set number of miles or hours or time. Sure, you can guesstimate mileage/time all you want, but understanding that bladders variably contract and expand due to age and temperature and that remaining fuel quantity will change depending on a host of other factors (ex. prevailing weather, headwind, tail wind or sidewind, how much aircraft load, altitude considerations, how much collective the pilot jockeys, etc) makes set mileage figures inaccurate (at the very least) and potentially deadly.
Of course, if the fuel gauge is simply bleeding, then you might have a problem.

I think some people are having difficulty adjusting to the bladder in a Prius, it's unlike the more straight line automobile fuel tank.

There is plenty of good advice from the senior members here, like multiply your overall mpg by 10 to get the mileage figure at which you should fuel up, or just fuel up at 2 pips (this is what I'm doing).

I hope this helps at least someone.

ZC1

[ZC1]

Originally Posted by moshe1436

I just completed a trip from Florida to New York and averaged 50.2 mpg overall with a loaded vehicle. On one leg of the trip I was approaching 450 miles on a tank of gas but the gas gauge still had 4 pips on it! I was panicky but made it to a station and put in only 8.3 gals. The MPG for that leg was 50.3. I seriously question the accuracy of the gauge and probably will never trust it again. Anyone else with this experience?

In your case, I'd bet my money that your car was literally on the verge of losing a pip. I would bet within 10 miles you would have lost that extra pip. I get that feeling.

ZC1

[moshe1436]

With 450 miles and 4 pips still on the meter, I think if I had waited until it was down to 2 pips I would have run out of gas by then. I was averaging around 51 mpg at that point. By multiplying 51 x 10 = 510 miles with 4 pips still on the meter doesn't make sense!

[Rokeby]

I fill up at two pips. I have not yet -- ~5500 mi. -- run out of gas. I have not
yet taken a trip "fully loaded." Nonetheless, this summer I probably will take
such a trip. I don't want to get caught out of gas on the highway. I'm getting
somewhat concerned.

It seems to me that when the car is "fully loaded," most of the new weight
will be aft and the suspension back there will settle more than at the front.
So, there would be the possibility that the combination of the in-tank float
valve and the two inclination sensors was not reading the fuel level correctly.

I suppose that the combination of an uncalibrated fore-aft inclination sensor
and a steep hill -- more likely on secondary roads than on a multi-lane
highway -- might cause the in-tank fuel gauge to show greatly more fuel than
it really is holding.

I'm wondering, would it be advisable at the beginning of the trip, with the
car "fully loaded," to reset the tank inclination sensors, and then fill the tank
to start the trip? Would doing this lead to a greater probability that the
guess gauge was... well, you know... kinda, sorta, pretty-much accurate?

************************************************** **************
Just for the fun of it, here follows information on resetting the inclination
sensors:

First, some information from the Toyota Tech Manual:
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"The direct acting fuel gauge is located in the sub tank. This gauge
consists of a pipe surrounded by a coil. A float in the pipe moves up and
down with changes in the fuel level. A magnet is attached to the float.
The up and down movement of the float causes a change in the
magnetic field. The flow of current through the coil creates a potential
difference and the resultant voltage is transmitted to the meter ECU.

"There are two inclination sensors located in the meter ECU to detect
vehicle longitudinal and latitudinal inclinations and to correct the fuel
level calculation. Corrections are made by the signals from the
inclination sensors and the ambient temperature sensor located in the
fuel tank.

"The inclinometer must be reset if the customer complains that they can
only pump a few gallons of gas into their tank or that they run out of
gas with three or four bars left on the fuel meter. The inclinometer
must also be reset if the Prius is refilled on an excessive slope or if the
fuel gauge becomes inaccurate. Please refer to the Prius Repair
Manual for the inclinometer calibration procedure. " [Emphasis added]
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And second, info on the procedure itself that was posted somewhile back:
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Bear68
Senior Member

... Anybody wanna reset the fuel gauge inclination sensor? Make sure your
fuel level is somewhere between 1/4 and 3/4, and temp should be about
70-90 F.

Step 1: PARK ON A LEVEL SURFACE!!!! If you are on a slope you will reset
the sensor to an incorrect level!!
Step 2: Press the ODO/trip button to turn the odometer to trip A
Step 3: Turn off the ignition and set the parking brake.
Step 4: DO NOT STEP ON THE BRAKE PEDAL! AT ALL! IT ISN"T NEEDED FOR
THIS PROCEDURE!!
Step 5: Press and hold the ODO/trip button and press the Power button
twice.
Step 6: Release and press the ODO/trip button three times
Release-Press-Release-Press-Release-Press and HOLD.

The Odometer on the combo meter should now be showing the normal
mileage, as you hold the ODO/trip button down, the reading should change.
Something along the lines of 650D0 or similar. The actual figures don't really
matter.

Step 7: Release and press the ODO/trip botton once more and HOLD it in.
The figure will change again. This time, only ONE digit will change.
650D0>65010 as an example.

Don't be afraid to try it. Even if it doesn't work, you won't goof anything up.
Try, try again. It sometimes takes a half dozen attempts before you get it
work right the first couple of times you do it. This only needs to be done
once in a while. I would recommend once every ten tanks or so. I usually
only do it when a customer has a fuel gauge issue. [Emphasis added.]

Takes a bit of practice but it resets the ECU to try to be more accurate in
it's estimation of your actual fuel level.

GOOD LUCK!!
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