Had my 2012 RRW for a month now and done a tad over 2100 miles so far. Naturally, I've been treating speed/revs/loading with 'respect' and have been watching my mpg (as reported by the computer).

Now, it says I have been getting an average of 29.6mpg since I reset Trip A when I picked the car up and 29.9mpg on Trip B that I reset when filling the tank previously.

However, for this last tankful, as a check I decided to do a manual calculation. I ran the tank from brimmed down to 1 mark above the red empty bar.

Brimming it again required ~72l of fuel for a total distance covered of 426 miles which by my calculation, gives 26.9mpg.

Blimey, thought I, this means the trip computer is 10%+ optimistic! 8ugger, that means my mpg is isn't really any better than my previous XK after all.

Also, when I filled the tank, it said I had a range left of 100 miles. Now in my ignorance, I thought I had an 85l tank, so having put in a little less than 72l, this meant there was around 13l (3 and a bit gallons) left so, maybe I'd been hitting the dizzying heights of 34mpg prior to pulling into the garage, which would make this 100 mile range about right.

BUT, I now read that I have 97l tank. So there wasn't 15l left, there was 25! That's 5.5 gallons! So my 100 mile range would equate to me getting 18.2mpg!

wtf?

29.9mpg?
26.9mpg?
18.2mpg?
and one mark above the red line equates to 5 gallons left?

I've never had a max range after filling up of greater than 525 miles (24.5mpg equivalent for 97l) - yet I've seen on here a 600 mile range reported

Hence my confusion!

Obviously I believe the 26.9mpg as it was 'independently' measured. But that trip computer (and fuel gauge) definitely sound worryingly inaccurate and misleading!

Should I accept this is just a case of TADTS and ignore what the trip readings are reporting? 2012 FFRR Westminster Orkney / Ivory and absolutely no pimp-glass!

Start using fuelly.com (see my sig - you can click on the image to go there) to monitor your fuel usage and mileage. A test on one tankful is probably not enough to get a consistent reading.

Also I understood it was a 100 litre tank, but that may have changed with later models. I wouldn't worry too much about what the OBC says about miles remaining, when it gets closer to zero it can fluctuate wildly depending on your very recent driving (even to the point of a major change in the number of miles left due to a short burst of acceleration). Get the range down to @ 5 miles and it gets even more interesting!

FWIW my OBC is usually within .1 of what fuelly comes up with. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Still a tad concerned that the OBC can apparently be over 10% optimistic!

Any other FFRR owners getting the same 'generous' mpg? 2012 FFRR Westminster Orkney / Ivory and absolutely no pimp-glass!

fill tank to brim, reset the mpg computer and drive, when you have reached a quarter tank ,refill and do a calculation..it should be the same'ish as the mpg readout..

[worked for me btw] ... - .- -.




Y. O. L. O.
.

The OBC MPG display can be calibrated to get it to display the correct figure...

It's an option in the hidden menus... (This MIGHT only apply to BMW based systems...)

Test function No. 20 – Entry of Correction Factor for Fuel Consumption l This function is locked and needs to be unlocked via the procedure in Function Test No. 19. This function allows for the query and alteration of a correction factor for fuel consumption values. Display and entry of the correction value is a decimal form per thousand. l 'KVBR: 0980' – this shows a correction factor of 980. l Entry of the correction factor is in the range of 750 to 1250. On production, the correction factor of 1000, corresponding to 1.000, is programmed into the EEPROM.

Adjustment of the correction factor is possible using the trip reset button.

Each press of the button decreases the factor by 1. When the minimum of 750 is reached, the display reverts to the maximum of 1250. If the trip reset button is pressed and held, the value is decreased in increments of 10 to shorten the setting time.

When the desired correction value is reached, entry is achieved by pressing the check control button. The display moves
to test function No. 21.

The new correction value is calculated from the actual average fuel consumption value and the currently
displayed correction factor.

The average fuel consumption is calculated by filling the fuel tank at a pump and dividing the litres used by the distance travelled on the fuel used. The correction factor must relate to units of L/100km.

The following formula must be used to calculate the correction value, where
X = calculated fuel consumption,
Y = fuel consumption recorded by on-board computer,
Z = currently displayed correction factor: (X ÷ Y) x Z = New correction value.

Last edited by Simes on 21st Oct 2012 10:29am. Edited 3 times in total

what the feck does all that mean Simon..  ... - .- -.




Y. O. L. O.
.

It means when you're selling it, you can adjust it to show you get 45mpg...