My first fill up and the "2" memory was bang on with Fuelly. Is the computer on Elegance spec more accurate than the normal Greenline. My previous Greenline was about 10% optimistic with its MPG reading.

My first fill up and the "2" memory was bang on with Fuelly. Is the computer on Elegance spec more accurate than the normal Greenline. My previous Greenline was about 10% optimistic with its MPG reading.

My poverty-spec 'S' is usually within 0.1 / 0.2 mpg of the actual - always measured to the third click-off.

My 1.4 S also agrees within 0.1mpg on refill - I also use third click! I was surprised because I had read on this forum that they are typically up to 10% over.

Must be luck of the draw. My Elegance was 7% out. Tolerance of the CO2 sensor, maybe?

Must be luck of the draw. My Elegance was 7% out. Tolerance of the CO2 sensor, maybe?

Displayed mpg is a function of distance covered / fuel used (from flow meter).

Mine reads about 17% too high.

Mine reads about 17% too high.

Ouch - you need someone with VCDS to re-calibrate it for you!

Mine reads about 17% too high.

Me too. Indicated 50mpg comes out at about 42mpg on Fuelly.

Ouch - you need someone with VCDS to re-calibrate it for you!

VCDS can only correct up to 15% each way but it would still be a vast improvement, particularly on the range (miles left) display.

Displayed mpg is a function of distance covered / fuel used (from flow meter).

My mistake, it just goes to show that anything you read on the internet is worth exactly what you pay for it! Though reading up on the subject (caveat: on the internet (for free)), on diesels a differential mass flow meter is used that measures total flow and then subtracts the pressure bypass regulator flow to give the net amount sent to the mechanical injectors. Petrols use the fuel injector duty cycle combined with a pressure measurement to calculate consumption. I'm sure I'll be corrected on that in due course.

Then, next time the old "instantaneous mpg readout" question comes up in the local's pub quiz I'll be sorted.

Edited 27 April, 201313 yr by artichoke273

I won't pretend to understand how these mpg calcs work but reading the above comments it sounds like petrol and diesel calculate consumption in different ways. So could it be that the petrol engines are reporting more accurately than the diesels? Mine is petrol (1.4) and is near enough spot on.

7% optimistic here, but since corrected with VCDS.

Mine was 10% optimistic before I calibrated it (with VCDS)

11% here over it's lifetime. Bloody rubbish and you have to question how it can be so off the mark from the factory. It was the same with my Mk II Octy. I now mentally knock 10% off when looking at the dash display.

The Wife's Fabia is pretty much spot on though.

Mine seems ok on average but I get trip readings from time to time that just dont add up

Took mine to south coast, all gentle stuff, range seemed to work but partial read outs must have been rubbish. Cruising on A35 showed 47 mpg Wandering back via Marlborough to Swindon saw the magic 50mpg. Down the M4 keeping revs to around 2250 I was looking forward to great things.

Brimming and putting data into Fuellog on my phone showed 40mpg - I was gob smacked and disappointed - previous Saab auto diesel would have given an easy 46. Car only done 7000 miles - will it get better?

Yes it will get better ours took at least 10k to start to loosen

I've done nearly 22k and not really changed that much since I got it new.

My Greenline is improving every week as the engine losens. Now at 9000 miles and mpg has improved by about 4mpg from new, that is with the same journey every day.

Just checked my last fill up of my greenline to see how accurate it is in comparison to the maxi dot. My trip 2 which I always reset prior to leaving the petrol station was reading 60.9. Put all the figures into my fuel app (aCar) and it came out at 61.7 mpg. Looks like mine certainly isn't optimistic. I always fill up to the first click and record in my fuel app.

Don't forget that we are back onto summer fuel now, so you should see slightly higher mpg just from the change in fuel.

Don't forget that we are back onto summer fuel now, so you should see slightly higher mpg just from the change in fuel.

Dont get me wrong, but over the last 15 years I've always noticed an increase in fuel economy as the ambient temperature rises. What I am saying is that the 2 figures I quoted are for the same tank of fuel. One for the maxi dot and one calculated by my fuel app. The difference being that my maxi dot figure is less than the one accurately calculated, which is normally the other way round.

Dont get me wrong, but over the last 15 years I've always noticed an increase in fuel economy as the ambient temperature rises. What I am saying is that the 2 figures I quoted are for the same tank of fuel. One for the maxi dot and one calculated by my fuel app. The difference being that my maxi dot figure is less than the one accurately calculated, which is normally the other way round.

Sorry, I forgot to quote pesmog's note. My point was that increasing mpg (through time) may also be down to the switch to summer fuel. I didn't mean it to apply to calculating difference between maxidot, and the physical calculation method.

I'll get me coat...

Edited 4 May, 201313 yr by JakeBlade

I'll get me coat...

Don't rush off, Jake - We knew what you meant! :yes:

Summer fuel?

Summer fuel?

Assume he's referring to anti-waxing additives added to most diesel fuels upon delivery to the filling station - may add less, or none, over summer months?