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Discussion Starter #1
Last time I filled the tank, I expected it would take more, so I tried slowing down the flow below the automatic shut-off pump lever position, and I got quite a lot more in the tank. The automatic shut-off was at about 36 litres, but when I squeezed the pump lever just enough to let the fuel flow, but not enough to get to the automatic shut-off, I got another 4 liters in (about one US gallon). I could have got more in, but stopped.

I've read here that doing this will stretch the bladder in the fuel tank. This may be true, but I find it a little hard to believe, as that would be a design flaw. On the other hand, I don't know why the pump would shut off when it is still possible to get another gallon in.

Does anyone have information on this?

After going about 860 km, (about 534 miles) at about 52 mpg average on the tank, the last pip has been blinking for about 27 km (16 miles). Therefore, I have used up about 10.5 US gallons. My mission is to get over 900 km, because people don't seem quite impressed enough when I tell them 750 km.
 

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Just as long as you realize that when you run out of gas Toyota gave you a phone number for you to call for roadside gas service as car will probably run no more than a mile on battery power alone. My suggestion when you are below quarter tank and you are "going for it" you might be smart to carry a gallon container of gas with you.
 

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Canadian Prius said:
Last time I filled the tank, I expected it would take more, so I tried slowing down the flow below the automatic shut-off pump lever position, and I got quite a lot more in the tank. The automatic shut-off was at about 36 litres, but when I squeezed the pump lever just enough to let the fuel flow, but not enough to get to the automatic shut-off, I got another 4 liters in (about one US gallon). I could have got more in, but stopped.

I've read here that doing this will stretch the bladder in the fuel tank. This may be true, but I find it a little hard to believe, as that would be a design flaw. On the other hand, I don't know why the pump would shut off when it is still possible to get another gallon in.

Does anyone have information on this?

After going about 860 km, (about 534 miles) at about 52 mpg average on the tank, the last pip has been blinking for about 27 km (16 miles). Therefore, I have used up about 10.5 US gallons. My mission is to get over 900 km, because people don't seem quite impressed enough when I tell them 750 km.
I too, have observed that if I slow down the pump flow, I can put more gas into my tank. Generally, when I start pumping, I already know approximately how much it should take. So I go "max" for the first half, then I let up on the pump, to let it slow down a bit.

When it clicks off, I (now) stop pumping. I learned recently that most pumps in the US have a safety feature that prevents further pumping after the first click-off. And whatever gas you are able to pump might well just be going back into the fuel pump. You can see that most pumps have two little holes in the tip. One is for fuel outflow. The other is for vapor collection. If you overpump, the extra gas just goes into the vapor collection hole, and not into your tank!

So overpumping is a waste of fuel. It would also invalidate my mileage calculations, because it's gas I have to record, but never get to burn.

But yes, I think slowing the pump down will let you put as much as .5 to 1.0 gallons more into the tank. I have observed this myself. I don't know why it is.

Oh yeah, remember that if you goof, and/or don't have a steady hand, the pump could click off prematurely. Then it may not pump anymore, no matter what you do. I think you have to reset it by starting a new transaction.
 

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Discussion Starter #4
zinzindorff9 said:
My suggestion when you are below quarter tank and you are "going for it" you might be smart to carry a gallon container of gas with you.
I'm way ahead of you! Yeah, I am carrying a gallon of gas ready for the moment of truth.

In fact, these days it might not be a bad idea for everyone to have a few spare gallons of gas in thier garage. A development to sudden runaway prices could result in panic buying and a shortage at the pumps. But if you do have some for emergencies, be sure to put in some gas preservative.
 

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Discussion Starter #5
BIF said:
If you overpump, the extra gas just goes into the vapor collection hole, and not into your tank!
Whew! Thanks for the information - I would have figured it out after pumping about fifty gallons - 'hmmmm.... wonder where all the gas is going?'
 

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Don't forget about...

BLADDER EFFECT

...because it is that time of year again!

Capacity of the tank will be reduced as the temperature drops, as much as 1.5 gallons (5.7 liters) in the extreme of winter. This is because the cold causes the bladder (which significantly reduces evaporative emissions) to shrink.
 

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I have been filling up by calculating how much gas I used based on the MFD, adjusting for error.

When I was trying to find the error amount, I originally calculated 3.6% (MFD higher than actual). Eventually after a couple of tanks, gas came out of the nozzle, but flowed back in. Next tank, gas was at the neck.

Readjusted for 2.6%, and that kept the same level, at the neck.

In all times, I had to continue pumping after the first click.

After determining that my 2.6% adjustment is about right, I put .25 gal less than calculated so as to not get to the very top as it had been.
Still have to go beyond that first click.

So, since I can see gas at times after the click, but othertimes not, at least here, gas going back to the station's pump is not my observation.
I can pretty much state the same for other cars I owned.

But then, we may not have the same recovery system that some high pollutionn states may have.
 

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Discussion Starter #9
Follow up:

I ran out of gas at 944 km (577 miles)
I filled the tank with 41.54 litres (10.97 US gallons)
The MFD read 4.6 l/100k, which meant I should have used 11.47 US gallons.
Therefore the MFD says I got 50 miles / US gallon, but calculating by gas replaced, I got 53 mpg.

The last pip started flashing at 833 km, so I got another 111 km (68 miles)on the flashing pip.

Most posters say the MFD overestimates mileage, but here it underestimated it by 6%. However, I agree that the difference of 0.5 of a gallon to fill the tank could be explained by many things, including difference in temperature, accuracy of pump, or how much I could squeeze in. I'm thinking the MFD was probably right.

When I ran out of gas I got an orange engine check light, and a red triangle with an exclamation mark in it shown in the dash lights. I also got an odd symbol in the upper left corner of the MFD like an outline of a car on a square, red background, with a perpendicular centre-line through the car. All these warnings stayed on the display for about three miles, and then all disappeared together, but not til I was thinking, 'What have I done to my neat car?' I guess that was a gentle slap on the wrist from Toyota.
 

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Canadian Prius said:
Most posters say the MFD overestimates mileage, but here it underestimated it by 6%. However, I agree that the difference of 0.5 of a gallon to fill the tank could be explained by many things, including difference in temperature, accuracy of pump, or how much I could squeeze in.
Across the 42 tanks from both the 2003 and 2004, I've seen a LOT of variation; usually the MFD is higher than calculated (sometimes significantly) - only seen it lower 3 times.
 

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Discussion Starter #11
TechnoMage said:
Across the 42 tanks from both the 2003 and 2004, I've seen a LOT of variation; usually the MFD is higher than calculated (sometimes significantly) - only seen it lower 3 times.
I would like to see someone do a real study on the accuracy of the MFD mileage. I have a feeling the MFP would be extremely accurate.

Maybe someone has done it the way that would give accurate figures... i.e. keeping track of exact gas purchases over, say, 25 tanks, starting with a full tank and ending with a full tank, and then doing one calculation over the 250 gallons or whatever and comparing it to the accumulated MFP readings. Other than that, there is too much inconsistency in what the real gas quantities are from tank to tank.
 

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Canadian Prius said:
Maybe someone has done it the way that would give accurate figures... i.e. keeping track of exact gas purchases over, say, 25 tanks, starting with a full tank and ending with a full tank, and then doing one calculation over the 250 gallons or whatever and comparing it to the accumulated MFP readings.
Sounds like exactly what I've been doing over 32 tanks and 296.084 gallons on my wife's 2003 Prius.

MFD Calc Diff
48.8 43.2 5.6
48.0 41.9 6.1
49.0 46.8 2.2
48.1 46.4 1.7
48.5 46.8 1.7
46.6 41.4 5.2
47.2 44.9 2.3
49.2 44.1 5.1
48.5 47.4 1.1
47.0 42.6 4.4
47.0 45.8 1.2
47.5 43.3 4.2
49.6 48.2 1.4
50.7 47.4 3.3
48.9 47.8 1.1
48.0 44.7 3.3
48.7 48.1 0.6
49.2 42.5 6.7
47.6 43.7 3.9
48.6 46.6 2.0
50.3 46.3 4.0
47.4 46.7 0.7
44.2 39.7 4.5
50.1 43.8 6.3
49.7 44.9 4.8
47.1 44.9 2.2
48.2 48.3 -0.1
46.4 44.0 2.4
45.0 42.6 2.4
47.0 49.1 -2.1
47.1 41.9 5.2
51.4 47.9 3.5

49.6 45.1 4.5 avg. over 32 tanks
 

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Yep, me too, only for 19 tanks so far...

http://home.cfl.rr.com/njfiorello/priuslog.xls

A brief description of the columns:
Code:
Columns:
A =Date tank was filled

B =Odometer total miles at time of fill-up
C =Odometer trip  (reset at each fill-up)

D =MFD Outside Temp at time of fill-up
E =MFD Average MPG - (reset at each fill-up)
F =MFD Gas - Calculated (Trip / MPG)

G =Tank - Gas - fuel put into tank
H =Tank - MPG - Calculated (Trip / Gals)

I =Variance - MPG - Calculated (MFD MPG - Tank MPG)
J =Variance - Gas - Calculated (MFD Gas - Tank Gas)
K =Variance - % - Calculated  (VAR MPG / Tank MPG)

L =Pump - Octaine of Gas
M =Pump - Price of Gas
N =Pump - Total Sale

O =Notes - Anything I felt like putting in

Totals Fields:
A1=Esoteric estimate of dollar savings based on 33 MPG Saturn SL2
C1=Total of all trip miles. A cross check for Column B
E1=Mean MFD MPG
H1=Mean Tank MPG
J1=Total Variance - Gas
K1=Total %Variance - 2.7% for those w/o Excel
M1=Mean gas price per gallon
N1=Total gas cost
 

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The variance over the 171 tanks (1,318 gallons) with my 2001 Prius was an overall 2.1 MPG difference.

http://john1701a.com/prius/spreadsheets/Prius-2001_MPG_Spreadsheet_Lifetime.xls ...note column "S".

The variance over the 56 tanks (454 gallons) with my 2004 Prius has been an overall 1.4 MPG difference.

http://john1701a.com/prius/spreadsheets/Prius-2004_MPG_Spreadsheet_Lifetime.xls ...note column "V".

I don't put too much stock in individual fill-up calculations since pump-error and bladder-effect have far too profound of an effect.
 

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john1701a said:
...I don't put too much stock in individual fill-up calculations since pump-error and bladder-effect have far too profound of an effect.
Agreed. Fuel economy is best calculated over MULTIPLE TANKS. This will mitigate the bladder effect and pump error and even the positions of Venus, Mars, and the hemline on that lady pumping gas across from your car. You didn't know about that last one, did you? :p

PS - John, Mel, and Mage, it's so cool when everybody can produce detailed mileage information to support their assertions. Way cool!
 

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It's all just wrong!

I had another one of those ideas that my shrink refers to as a paranoid delusion.

Toyota has already sold me the car, so there isn't any tangible gain for them to intentionally skew the MFD estimates towards optimism.

However, the convenience store owner selling me the fuel has something to gain if the pump says 1.00 gallons when it's really spat 0.97 gallons into my tank. His fuel profit margin is increased by 3%

We could be seeing evidence of a world wide conspiracy here.
 

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I just drove from Brisbane to sydney on 1 tank the last bar was blinking for the last 30 minutes, and I had a can in the back of spare fuel, but I made it without having to use it.

the trip meter said 999.9 km from my driveway to my parents in sydney. and I filled up about 4 km from my place.
 

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Discussion Starter #18
Roger said:
the trip meter said 999.9 km from my driveway to my parents in sydney. and I filled up about 4 km from my place.
Does that mean that there isn't room to show more than 999.9? i.e. that it can't show 1000.1?

By the way, that is a great distance on a tank of fuel! Not only do we get to go so far between fill-ups, we have so many fewer inconveniences of doing that task.
 

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no, funnily enough, that was the distance. Dad joked that I should have done a lap around the block or made a wrong turn to make it exactly 1000 between our houses :)
 

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fuel economy

Toyota web site says traditional mpg calculaton (miles driven /gals pumped) is inaccurate for Prius, due to effects of things many of you have already noted...bladder effect, temp on bladder effect, varying pump rates effect on bladder. They say to use the MFD reading.

I see no reason to suspect the accuracy of the MFD reading. That is what I quote as my mpg, even tho I do the miles/gal calc to observe the difference.
 
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