Keen with my relatively new to me Octy II to work out true MPG I found an anomaly

I was seeing the economy for single journeys go up to 79mpg+ ( warm night 1am -= really gentle driving, not having to stop at any lights etc..)

When refuelling, the computer said 64.5 average but when brimming and calculating I got 53mpg (More what I'd expect) using the total from the trip computer that I zero at each fill up. I double checked that I'd written the trip miles down correctly by subtracting the odometer totals and discovered that there was 5% difference. The trip miles always read between 4.4. and 6.4% less than the odometer miles!

Is this a known problem?

For others watching your fuel you may be getting 5% more mpg than you thought you were (assuming the odo's correct not the trip!)

Nick

The average mpg readout is known for being optimistic, if you know how much it's out by it can be adjusted using VAG-COM. I highly doubt you were actually anywhere near 79mpg, you don't think you might have been reading the instantaneous readout in error by any chance?

It's very suprising that the trip miles and odometer miles are different. I guess you could get a small discrepancy if you zero the trip meter when the odometer is at, say x.5 miles. But I would have thought that the the two counters were served by the same electronic counter. This call for an experiment!

I've noticed something similar between the two average MPG's in Maxidot, reset both "1" and "2" and there is almost always a difference at the other end of the trip...perhaps one takes the odo and the other takes the trip mileage?

Just checked mine. Have done 767 miles since resetting trip and maxidot; odometer, trip and maxidot all show the same reading.

I'm going to check it against my Garmin satnav on the next long journey and see what difference that produces. I won't be surprised if it reads considerably less.

Car manufacturers are notorius in making you think you are going faster and further than you really are.

In theory the sat nav should be more accurate as it's not influenced by things such as the rolling radius of the tyres which can produce a 2% difference between new and worn, and the tolerances that are allowed in speedometers.

My speedo overreads by 4% so I'm quite expecting the mileometer to be out by the same amount.

Always reset both and get the same mileage at fill up time. Last fill up indicated 59mpg over 616, but in reality it was 52.8mpg which is still very good and only 0.2 from my pb. I know the computer is out but I know getting an average of 60mpg will return 53mpg which is what I aim for. Warm weather and holidays help and I do still stick my toe down on a 2 mile dc on my commute

I've noticed the same thing on my 2005 A4 1.9tdi - the odometer, trip & fuel computer all show different mileages when you go on a long journey. Interestingly, TomTom comes up with yet another figure so I have no idea which of the 4 is accurate, if any of them are...

I've just measured over 465 mies. The trip computer showed 50.8 and my own calc spookily was exactly 50.8 too!