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Model specific boards => Golf mk7 => Topic started by: Redalltrack on 12 January 2018, 15:25

Title: Accuracy of fuel consumption on mfd
Post by: Redalltrack on 12 January 2018, 15:25: Apologies if this has been discussed previously.
I am a happy owner of a mk7 golf and find the various stats indicated in the mdf quite useful - particularly the ave mpg figure.
From reading various posts, it appears that some owners treat the mdf figures as gospel. Although not normally a stickler for recording such data I decided to do a few brimful to brimful checks to ascertain the accuracy of the mfd figures and satisfy my curiosity. I have found the mfd figure to be 5-7% optimistic which I do not think is too bad. I have had other makes of car in which the mdf figures have been have so inaccurate to render them useless.
I assume this discrepancy can be adjusted in the VCD's. As my car will be having a service shortly I was wondering if I could ask the VW dealer to recalibrate the mfd accordingly or is this a complete no no!
Any advice/experience would be appreciated.
Title: Re: Accuracy of fuel consumption on mfd
Post by: Watts on 12 January 2018, 15:44: I've checked mine a couple of times and found it to be spot-on! I was rather surprised. So now I do take it as gospel.
Title: Re: Accuracy of fuel consumption on mfd
Post by: fredgroves on 12 January 2018, 15:57: Even your "brim" definition is variable, unless you truly fill it until you can see it overrun the filler.

I'd have also thought that temperature variations could also account for differences in volume too...
Title: Re: Accuracy of fuel consumption on mfd
Post by: Daz Auto on 12 January 2018, 16:41: Quote from: fredgroves on 12 January 2018, 15:57
Even your "brim" definition is variable, unless you truly fill it until you can see it overrun the filler.

I'd have also thought that temperature variations could also account for differences in volume too...
This is a myth. The fuel underground is at a relatively constant temperature. So it makes no significant difference.

If it is a diesel, it is really hard to fill to the brim with the new mis-fuel device fitted.

I did a few calculations on my petrol car and found I was getting 35mpg. That's what the computer said too. So yes, it appears quite accurate.

It is funny watching all the members of an Audi forum bang on about how economical there Audi S3's are. Some of them actually believe their cars will do 40mpg because the computer says so. Most of them are getting around 350 miles to the tank which is actually around 30 mpg. "but the computer says..." :rolleyes: I told one guy to try and drive 12x40 = 480 miles in his S3 on one tank and let me know how he got on. :evil:

This week , the fuel light had not come on and I put 47 litres in the car (not to the brim). The manual says 5lt fuel reserve. So I must have at least a 52 ltr fuel tank :laugh:
Title: Re: Accuracy of fuel consumption on mfd
Post by: dubber36 on 12 January 2018, 17:05: Quote from: Daz Auto on 12 January 2018, 16:41

This week , the fuel light had not come on and I put 47 litres in the car (not to the brim). The manual says 5lt fuel reserve. So I must have at least a 52 ltr fuel tank :laugh:

This assumes the pump is accurate.

Many years ago there used to be just one fuel station in our little town. He could virtually name his price. A supermarket opened up and started selling fuel much cheaper. He dropped his prices to match, so I went to him and filled my Mk4 Golf up. That has a 55 litre tank, but according to his pump, I put over 70 litres in it.
Title: Re: Accuracy of fuel consumption on mfd
Post by: fredgroves on 12 January 2018, 17:09: Quote from: dubber36 on 12 January 2018, 17:05
Quote from: Daz Auto on 12 January 2018, 16:41

This week , the fuel light had not come on and I put 47 litres in the car (not to the brim). The manual says 5lt fuel reserve. So I must have at least a 52 ltr fuel tank :laugh:

This assumes the pump is accurate.

Many years ago there used to be just one fuel station in our little town. He could virtually name his price. A supermarket opened up and started selling fuel much cheaper. He dropped his prices to match, so I went to him and filled my Mk4 Golf up. That has a 55 litre tank, but according to his pump, I put over 70 litres in it.

Thats highly illegal under the Weights and Measures Act:

http://www.coventry.gov.uk/info/30/trading_standards/350/weights_and_measures
Title: Re: Accuracy of fuel consumption on mfd
Post by: I wanted a GTi on 12 January 2018, 18:55: I tried mine when I got it and it was between 1 and 2mpg out.
Title: Re: Accuracy of fuel consumption on mfd
Post by: itavaltalainen on 12 January 2018, 20:34: Mine is accurate to around 2-3%.
Title: Re: Accuracy of fuel consumption on mfd
Post by: robtt on 13 January 2018, 17:44: I check mine brim to brim most fill ups and the read out is very accurate .
Title: Re: Accuracy of fuel consumption on mfd
Post by: Gnasher on 13 January 2018, 18:18: Another thing to think about is the effect of having a tuning box fitted - these allegedly make the fuel computer more optimistic.

Never checked mine against it - I don't think I could have handled the disappointment!
Title: Re: Accuracy of fuel consumption on mfd
Post by: mcmaddy on 13 January 2018, 18:20: Yes tuning boxes will affect MFD readout by about as much as 10%.
Title: Re: Accuracy of fuel consumption on mfd
Post by: I wanted a GTi on 13 January 2018, 19:51: Quote from: Gnasher on 13 January 2018, 18:18
Another thing to think about is the effect of having a tuning box fitted - these allegedly make the fuel computer more optimistic.

Never checked mine against it - I don't think I could have handled the disappointment!

I checked mine with the tuning box fitted and it was :laugh:

Can't remember what the exact figures were but it was out by a fair bit.
Title: Re: Accuracy of fuel consumption on mfd
Post by: mcmaddy on 14 January 2018, 09:08: The tuning box is fooling the car into thinking it's using less fuel as they don't connect to anything to do with fuel sensors etc.