To work out miles per gallon from miles and litres consumed.

 

Divide litres by 4.54 to give gallons so 53.19 litres = 11.715 gallons.

 

Miles per gallon, the clue is in the "per" so you did 556 miles per 11.715 gallons.

 

Divide 556 miles by 11.715 gallons equals 47.5 mpg.

 

Probably an accurate figure but only if you patiently brimmed your tank the time before, they are such a slow filler the difference can easily be 7 litres if you are rushed, the next refill done in the same manner will give you a definitive figure.

 

Lets use your existing ones for the example to answer your question re VCDS.

 

You are getting 47.5 mpg but the MFD says 36 mpg = overestimating the consumption.

 

47.5 - 36 = difference of 11.5

 

11.5 divided by (computed) 36 x 100 = 32% over-read

 

I think that may be too much for VCDS to be corrected but the correct way would be use a correction factor of 1.32.

Wow ! 

When a brimmed it a meant it spilled out and down covering the wheel in diesel totaly by accident.

LOL 

So the next question is you say correction factor of 1.32 whats that sorry am not that clever 

Do the same next time to get an accurate figure

 

I would have to look in VCDS, see how I corrected mine to give you the correct terms and procedure, I am not the best at explaining things especially without the correct terms and VCDS often has confusing terms like "torsion value"

 

Mine was over-reading by 13% IIRC saying something like 62 mpg whereas my brim to brim calculation was 55mpg so I had to use a correction factor of 89% and not the 87% you might think but thats a different maths lesson.

 

And it is possible that I have got both those correction factors the wrong way round, VCDS is often counter-intuitive and I would have to read the notes rather than relying on my memory.

Thanks

Its a lot easier do the math the other way, less conversions to remember -

 

Distance divided by the fuel put in

556 / 53.19 = 10.45mls/litre

 

Multiply by 4.546 (litres in a uk gallon)

10.45 x 4.546 = 47.519.  

Call it 47.5mpg, even 47 just to allow for inaccuracies.

 

On that basis a full tank range is

10.45x55 = 574.75miles

Thats not bad..

Thanks very much 

Need to go back to school lol for maths lessons.

2 hours ago, mac11irl said:

Its a lot easier do the math the other way, less conversions to remember -

 

 

You have 2 calculations and one conversion to remember as did I, to me both methods are valid and as easy as each other, horses for courses, what have I missed?

 

Math is easier to type than Maths I give you that

Edited 22 August, 20196 yr by J.R.

3 hours ago, J.R. said:

 

You have 2 calculations and one conversion to remember as did I, to me both methods are valid and as easy as each other, horses for courses, what have I missed?

 

Math is easier to type than Maths I give you that

 

Yeah, i just find keeping it metric for a bit longer easier

 

Well me light come on at 546.9miles.

Number 2 is saying 39.2mpg.

Number 1 is saying 38.7mpg on the MFD. 

On the MFD it said a had 25 miles left to go.

A put 49.91 litres in to brim to get the 546.9 miles 

So to brim it again a put 53.89 litres in see how many miles a get this time.

So a think a have worked it out a was getting 51.5mpg  which a don't think that's right 

Edited 31 August, 20196 yr by Taximan1978

12 hours ago, Taximan1978 said:

Well me light come on at 546.9miles.

Number 2 is saying 39.2mpg.

Number 1 is saying 38.7mpg on the MFD. 

On the MFD it said a had 25 miles left to go.

A put 49.91 litres in to brim to get the 546.9 miles 

So to brim it again a put 53.89 litres in see how many miles a get this time.

So a think a have worked it out a was getting 51.5mpg  which a don't think that's right 

So when you refilled to the brim at 546.9 miles did you put in 49.91 litres (or was that the previous fill up) or 53.89 litres?

 

It will be more accurate on the next fill up but using your second figure gives 46.07 mpg or 49.75 mpg using the first.

Yes that was the previous fill up the 53.89 litres is what ave just put in to 're brim it but even now the MFD is still reading 38.9 on number 2.

Thanks for the reply.

Number 2 trip resets itself when the distance or other parameters exceed its memory limit. So 38.9 could be based on a couple of short journeys.

If you use this it is better to also read the miles and time to see if they are long enough to be a fair estimate.

 

Best way is still to ignore trip1 and trip2. Instead use the trip distance which is reset with the knob on the speedo, resetting it to zero when you fill up.

Thanks for the reply.

So just an update 're brimmed the tank it took another 53.19 litres.

on the trip meter a done 546.6 miles and on the MFD display said a had 25 miles left to go.

The fuel light came on at 527.7 miles.

The MFD display was displaying 38.5 on trip 2.

Well that calculates as 46.7mpg..

 

Did you reset trip 2 after the last fill up?

Yes 38.5 MPG that's what it was reading.

 

So let's say the car is right but the MFD is wrong how do a correct it.

Done the calibration but doesn't seem to do anything in the past.

Not a clue how to do the mfd, but..

@Tech1e is a clever guy who may know

 

Cheers 

It's been years since I recalibrated one of these but from memory you can only adjust the MPG display by a maximum of 15% in either direction. Yours is slightly more inaccurate than 15% though so you will never be able to get it absolutely spot on. Basically the default value is 100 and if I remember correctly you increase that value to correct an overly optimistic MPG display, and reduce it to correct a pessimistic MPG display (someone please correct me if I've got that the wrong way round!). The lowest it will go is 85 and the highest is 115.

 

So, to get your display as accurate as it can be you would need to set the value to 85.

 

Edited 7 September, 20196 yr by nick74

Thanks for that

So this is what the dash says just another update.