Which is Better Calculated or Screen?

I think the only way we could be sure of being cheated is by bringing in our own calibrated gallon jugs.

 

i did report it about Oct i believe. last time i was in the area i checked the station and inspection sticker still said "april 2000". that was about 2 months ago i think.

 

remember that most gas pumps are temperature corrected to I thinks it's 50F. So it'll change from season to season as the ground heats and cools and as the tanker brings in fuel at a different temperature. The pump manufacture's all claim over a year it all balances out.

 

I have found another factor which comes into play. The self stopping gas pump handles are not all alike. Having to jam them into a closely fitting rubber sleeve seems to affect some of them strangely. I've had to switch pumps a number of times as some of the handles simply would not pump any gas into the tank even though the tank was half empty. Therefore I question the point at which they stop pumping versus the fullness of the bladder.

 

I found that over the course of the past year my spreadsheet shows the annualy average to be within 0.1% of each other, although each individual tank differs and has never agreed for me. For me that means that they are close enough for what I need it for (long term trending).

 

My MPGs are off about 1 MPG between calc. vs MFD computer.


I found this interesting:


http://www.fredericknewspost.com/sections/...m?StoryID=42454

 

Hey guess what?

i received a letter stating that my issue with the short pump had been addressed and although some pumps needed calibration, none were shown to be off far enough to warrant anything other than a warning to the station to comply within 30 days.

so, iow, dont know if the pump was actually short or not... that sucks.

 

According to my records I am usually between 0.2 - 8.2 mpg off but on avg of 2.2 and median of 1.9 mpg. That is about 4% of my lifetime average. That is not too much to bother me although my wife is rolling her eyes that I even have the data to calculate this (or the fact my spreadsheet already does this).

 

Yesterday when I filled up it took 6.2 gallons to get to the shut off which would of given me a calculated average of like 74mpg. I went into the store to buy some lunch. When I came back out I was able to put in another 2.8 gallons. Now my mpg was 51.1.

My screen average was 48.7mpg.

 

I see much variance between the computer and calculated from tank to tank, sometimes my calculated is as much as 8 mpg lower than the screen calculation. However, when I look at lifetime mpg, I average about a 2 mpg difference, with calculated being lower than the computer. Considering I am getting 150% of the mpg of my last car, I am not complaining!

Year to date Avg 2080 miles
43.701 gallons
47.6 mpg calculate
49.52 mpg computer

Only once have I seen calculated exceed puter by more than 2-3 mpg.

 

mine also used to be higher for the computer verses pump calculation, but as time went on, the gasp continued to get smaller and smaller.

i am fairly sure that the accuracy of the Prius' computer has allowed me to compare the generousity of the gas pumps in my area which allowed me to narrow down my selection only to the pumps that give me the best mileage. (this is of course due to the lack of action by the State dept of Weights and Measures and their Mandate to calibrate all gas pumps in the state every 3 years. the most recent pump i use was last calibrated in April 2000.) this of course has probably tainted my mileage figures... but i can live with that...hehehe

this is the reason why now my calculated pump readings have slowly overtaken and past the computer readings which i still consider to be the most accurate. i know the good times are running out and i am very interested to see how the pumps will do right after being calibrated when they will supposedly be the most accurate.

 

I'm with the "total miles driven / total gallons pumped" crowd for a TRUE lifetime. However, as others have said, there can be too much variability from 1 tank to the next to use the calculated value for lifetime until you have gone through the gas station many times.

My MFD lifetime is maybe 2% higher than my calculated (over 10K miles). However the current tank MFD value is a very good indicator of how much gas you SHOULD be able to pump in. If you've driven 500 miles and the MFD says 50 MPG, pump until you get about 10 gallons in, it can't be less or the pump is WAY off.

I expect if you always stop at the first auto shutoff, your lifetime mileage will not change, but the total miles you can drive on a tank will be down. Mine would probably be 100 miles less given it usually kicks off at about 8.5 gallons. If I'm doing normal commuting, I fill about 10-15 miles past "1 bar flashing". If I fill before the flash it is because I am going on a long trip.