Accurate mpg???

[Shacky13]

Owned my Octavia 1.9 tdi 3 months now and totally unsure on the accuracy of the mpg average and the miles left with fuel remaing .... looking at mpg ....generally getting around 60mpg on my trips to work ...my old car claimed around 48 ... yet the old car seemed cheaper to run on fuel ... and then the computer miles left thing .... say I fill up to around 3/4 a tank ...it'll say I have 620 miles of fuel left .... drive 25 miles to work and check again ..580 ...always get around 200 miles less than the computer says for the fuel I've put in......any thoughts? 

[Golf-Fiend]

It's all lies. Lies I say! Only way is proper measuring. Fill tank. Drive. A lot. Fill tank. Note litres. Note miles driven. Do the maths. You'll have an answer. 

[Metblackrat]

The problem is your odometer is up to 10% out and the fuel pumps have found to be up to 4% out. Given this, your calculations are also going to be out. Despite what anyone may try to tell you, unless you have access to some pretty expensive calibrated equipment, it's pointless to try to work out what your consumption is. 

[andy-fisher]

I nearly always use the same pump at the same garage every fuel up. My car lies on the optimistic side showing great readings on the display. My best ever is 71.3mpg calculated from tank to tank but I was trying hard to get that and it was with summer fuel and a good couple of runs. My all time average is shown in my signature. The computer is only a guide, I don't rely on it. I also find that I get more miles to the first half a tank than I do the second, maybe proving there are too many variables that the computer doesn't account for.

Edited 1 March, 2017 by andy-fisher

[Shacky13]

1 hour ago, andy-fisher said:

I nearly always use the same pump at the same garage every fuel up. My car lies on the optimistic side showing great readings on the display. My best ever is 71.3mpg calculated from tank to tank but I was trying hard to get that and it was with summer fuel and a good couple of runs. My all time average is shown in my signature. The computer is only a guide, I don't rely on it. I also find that I get more miles to the first half a tank than I do the second, maybe proving there are too many variables that the computer doesn't account for.

So so true about the two halves of tank ...from full to half takes eons...below half it falls like a stone with every trip .... I had a vw bora before the Skoda and I'm sure that had a way more honest and accurate ish mpg but also the gauge fell like a stone below half a tank 

[Jevpls]

A few people have said that according to their observations these cars consume ~8% more then the computer shows.

But you can test it yourself easy:

1) fill the tank full;

2) reset the trip mileage counter;

3) drive a lot and then fill again (full). Then you have the accurate mileage and you know how much fuel you have added. Simple maths to get the MPG.

 

Note: the average MPG on computer resets after 2 hours or so. There is a way to switch to a mode that allows it to reset after 4 days or so but I think that's only on a car with Maxidot only.

[zeffania]

I tweaked mine using VCDS over a number of runs and it is still out. I usually get 57-58 in the car, but it is more like 54-55 real time so not far off. I think it was 10-12% out when I did the test all those years ago

[Shacky13]

Ok well I think my computer is broken.... arriving at work this morning it said 215 miles of fuel left....lashing with rain so go sit in car... start it up.... 165 miles left!!!! Without moving!!!! 15 minutes later 150 miles left!!!! Still not gone anywhere!! 

[AVHreplica]

Mike's right!  

Do not blame the trip computers...they are not so "broken" and they must not be...

Factories do not cheat us so much though....

The measurements/info they get and the way how they calculate it is a complex of data and numbers and maths. We need to examine it and understand well the way they work.

 

For example standing idle, it consumes fuel in a way "not economical" although we think that from the moment the gas pedal is not pressed means should be economical.  The computer sees car is not moving and this increases the fuel thus reducing mpg. So as many minutes this happens it will reduce the mpg.

 

Another example, the computer (re)calculates the information it continuously gathers in time of every 4-5 secs which this also means that a lot of factors play their roll of the fuel consumption and so in the mpg like driver's attitude, overall electrical consumption (lights, clima, audio sys, rainwipers etc.), direction of wind flowing in the car, and many others so in a sucheck heavy conditions of driving the car should probably reduce mpg...in the opposite should increase etc...

Driving up a mountain is quite different from rolling then down to straight ground....

 

Conclusion:  for a very short of distance (or time) computer may indicate low mileage with the tank's remaining.........while after another short of distance (or time) this can be increased!!  (or decrease more!!!! due to the above factors referred....)

 

For testing and curiosity, try to be as soft driver (smooth accelerations and driving stability, easy breaks on, turn off electrical components which are not really needed etc.)  and behave your vehicle in another way.

Do this for some days and you should be able  not to see big differences in the values of your trip computers and mpg will be kept in a logical point of area.

 

I have managed and understood the above and I do not have problems with my trip computer - I'm keen on it and I work with it ok. 

[dilksie]

On 02/03/2017 at 10:54, Jevpls said:

A few people have said that according to their observations these cars consume ~8% more then the computer shows.

But you can test it yourself easy:

1) fill the tank full;

2) reset the trip mileage counter;

3) drive a lot and then fill again (full). Then you have the accurate mileage and you know how much fuel you have added. Simple maths to get the MPG.

 

Note: the average MPG on computer resets after 2 hours or so. There is a way to switch to a mode that allows it to reset after 4 days or so but I think that's only on a car with Maxidot only.

 

If you look at the average MPG reading on the display you will see a small number in the corner. 1 = trip consumption which automatically resets after 2 hrs. 2 = long term average which will only reset when you press the reset button (or the battery goes flat) to swap modes you press the button under the wiper stalk. to reset press and hold this button. This works on non maxidot displays as well.

[Auric Goldfinger]

On 01/03/2017 at 21:34, Metblackrat said:

The problem is your odometer is up to 10% out and the fuel pumps have found to be up to 4% out.

 

So we are actually paying for 4% of the fuel  at the pumps that we ain't getting it...........

[dilksie]

21 minutes ago, Auric Goldfinger said:

 

So we are actually paying for 4% of the fuel  at the pumps that we ain't getting it...........

 

Or you could be getting 4% extra fuel!! (but I very much doubt it)

[chimaera]

If you want to get a handle on how accurate the reported economy from the MFD is, reset MFD 2 when you fill up. It will record your average economy for the tank, which you can note down and compare to the manual calculation. Over successive fillups it will give you an indication of how accurate it is. Using VCDS you can correct this in one of the adaptation channels in the instrument cluster. This calibration is subject to variables you may not be able to control but it's still an improvement.

 

The calibration on the fuel gauge is not linear. It drops more slowly in the top half of the needle range than the bottom half. No idea why - you'd have to ask the engineers in Wolfsburg about it. At a guess I'd say there's a bunch of ergonomics/human factors theory behind it. There's also a bunch of signal damping at work with it, so it's not swaying up and down as fuel sloshes around in the tank during cornering, braking, etc.

 

The temperature gauge is not accurate either - it'll show 90 *C from about 75-105 *C actual coolant temperature. People apparently get freaked out by the temperature needle moving around so that deadzone was put in there.