How accurate is the MPG indicator.??

[Jazzik]

You want accurate MPG? Use (for example) this: https://www.spritmonitor.de/en/

Easy:
Use Spritmonitor.de on the road with your Android- or Apple-smartphone and the Spritmonitor.de app! Enter new fuelings right at the gas station.

Spritmonitor is just a calculation tool, the accuracy of the results depends on the accuracy of the data you enter. Sources of error can be the accuracy of measuring the fuel added (eg brimming the filler pipe in exactly the same way every time), and that the odometer reading can be a few % out.

Sure, but if you run the calculation over several fill-ups then the vagaries will be ironed out and the overall average will be very close to real consumption. Certainly accurate for comparison purposes.

Why would you like to know what the exact consumption is over 1 trip of (for example) 17, 170 or even 1700 miles?
I use Spritmonitor for more than 13 years. Three different cars. I know exactly what the consumption of these 3 (my) cars is.
The average consumption of our current car measured over more than 4 years can be seen next to this post.

[E27006]

The display gives figures  for mpg in floating point to a tenth of an mpg, eg  60.7, 60.8, 60.9  mpg,  this implies the measurement of fuel used and distance travelled  is accurately  measured to less than 1% error of  both variables,
I do not believe the measurement  of fuel consumed and distance travelled is so precise and accurately  measured  we can  trust the figure to a tenth of an mpg,  I believe even quoting mpg in integers    such as59,  60 or 61 mpg is beyond the capacity of the measuring system, probably rounding to figures in increments of 5 mpg , 55, 60, 65  are more credible for the measuring system

 

[guest9814]

No one can check accuracy of MPG indicator when using sprittmonitor without knowlege of accuracy of fuel pump on gas station.
They can sometime lie, for example - you car low fuel lamp lit, you enter gas station and get 40l of fuel in tank that can "hold" 40l (wait moment i have at last 5l in tank, how i can get 40l ?) , tank actualy can hold more fuel but filling it fully wery dangerus to do, this wil kill charcoal canister at last.
next time in same situation you enter another gas station our another fuel pump on same gas station and get only 35l.
Some gas station can fraud some ammount of fuel when driver filling tank to full, but when filling fixed ammount of fuel up to 10l you will get exactly wat you pay for.
Some have badly ajusted stopper on pump (so it can stop filling tank sonner or later)

[Downsizer]

Why is there a consistent variation?

It must be designed that way.  I think the measurement of fuel consumed is based on regular sampling and it’s clearly in the maker’s interests to err on the side of flattering the consumption, making us all feel better.  I don’t suppose there are any regulations specifying accuracy as it is not a safety issue.

[Expatman]

To check the overall average fuel consumption you don’t always need to fill to brim. As long as you start full and end full then it doesn’t matter how much you put in in-between, note how much and mileometer reading. I have checked fuel consumption since new for my present Yeti and over 36,000 miles it has averaged 44.82 MPG, worse was 35.4 and best was 47.2. Worse was a 400 mile high speed dash to Cornwall against a head wind and best was dawdling around Dorset for a week on holiday.
Data entered on Excel spreadsheet - okay a bit anal I know!!!

[Kremmen]

Not at all, I used to do that when I commuted at 11k miles a year but now that I only do about 2k miles a year I don't bother.

[guest4871]

Why is there a consistent variation?

It must be designed that way.  I think the measurement of fuel consumed is based on regular sampling and it’s clearly in the maker’s interests to err on the side of flattering the consumption, making us all feel better.  I don’t suppose there are any regulations specifying accuracy as it is not a safety issue.

The error on the fibometer seems to be quite closely related to the speedometer over read. Both over reading about 4/5%.

Is the false calculation of petrol consumption perhaps based on a false reading of speed?

Remind me, why does the speedometer over read?

[peteo48]

Not at all, I used to do that when I commuted at 11k miles a year but now that I only do about 2k miles a year I don't bother.

That's about my mileage give or take. This relegates fuel costs to a secondary consideration - certainly compared to depreciation.

[nowster]

No one can check accuracy of MPG indicator when using sprittmonitor without knowlege of accuracy of fuel pump on gas station.
They can sometime lie, for example - you car low fuel lamp lit, you enter gas station and get 40l of fuel in tank that can "hold" 40l (wait moment i have at last 5l in tank, how i can get 40l ?) , tank actualy can hold more fuel but filling it fully wery dangerus to do, this wil kill charcoal canister at last.
next time in same situation you enter another gas station our another fuel pump on same gas station and get only 35l.
Some gas station can fraud some ammount of fuel when driver filling tank to full, but when filling fixed ammount of fuel up to 10l you will get exactly wat you pay for.
Some have badly ajusted stopper on pump (so it can stop filling tank sonner or later)

The weights and measures legislation in your country must be particularly lax.

[Jazzik]

The weights and measures legislation in your country must be particularly lax.

...or maybe non-existent?
It is of course also possible that Roman has no idea that something like weights and measures legislation exists in his country...

[guest9814]

The weights and measures legislation in your country must be particularly lax.

...or maybe non-existent?
It is of course also possible that Roman has no idea that something like weights and measures legislation exists in his country...

Sometimes our police checking gas stations, but gas station operators have now advanced tech to fraud only if someone fill full tank or more then 10l, if someone want to check accuracy of fuel pump at gas station uses  special measurement 10l canister with temperature correction marks, so when someone filling only 10 liters program that used to fraud fuel not adding readings to pump meter.
And any complain about fuel tank capacity not working because they sais tank can hold more than specified......

[guest9814]

Example one week ago i drive from work, and on flat road low fuel warning come, with something like 70km remaining to "empty" , our reserve fuel is around 5.3l
Gas station that i using always is 1km from my workplace, i entered gas station and filled full tank - reading 36.5l....
But if I understand right i sill not run on reserve fuel.
So if in tank actually more than 5l, or that pump slightly overfilled my tank or i pay for more fuel than I get.

[Jazzik]

Sometimes our police checking gas stations, but gas station operators have now advanced tech to fraud only if someone fill full tank or more then 10l, if someone want to check accuracy of fuel pump at gas station uses  special measurement 10l canister with temperature correction marks, so when someone filling only 10 liters program that used to fraud fuel not adding readings to pump meter.
And any complain about fuel tank capacity not working because they sais tank can hold more than specified......

So if I will ever drive around in Israel it will be 9.99 liters at gas station 1, then drive on to gas station 2, there again 9.99 liters and so on and so on... I don't like to be cheated!

[Downsizer]

The error on the fibometer seems to be quite closely related to the speedometer over read. Both over reading about 4/5%.

Is the false calculation of petrol consumption perhaps based on a false reading of speed?

Remind me, why does the speedometer over read?

I think the distance travelled part of the fuel consumption calculation is based on the odometer reading, not the speedometer.  Speedometers read high to eliminate the legal defence of “But my speedo reading was only 70 your worship”!

[E27006]

Speed ==  distance / time.
Distance == speed x time.
The basic signal is Vss  which is derived from a wheel hub sensor  counting pulses  of a toothed ring on the hub as the hub rotates. Vss is processed within the ECU for several other functions of the car such as the power steering and possibly the ABS