Mpg on dash how accurate ?

[Optimus prime]

How accurate is the mpg figure displayed in the instrument cluster ? My Bmw was way out but not sure about the E63?

Thanks

 

[paterson12]

How accurate is the mpg figure displayed in the instrument cluster ? My Bmw was way out but not sure about the E63?

Thanks

My CL55 Kompressor is actually quite accurate at 16 mpg. My previous W204 and my current Bmw where way out also.

 

[noy91]

Mine's usually within 5% on the few tanks I do a proper comparison on

 

[wemorgan]

You can calculate yourself by a brim to brim test.
Mine only shows a 1mpg deviation to the above method.

 

[Optimus prime]

You can calculate yourself buy a brim to brim test. Mine only shows a 1mpg deviation to the above method.

Yes that's what I normally do but it is nice to know that the displayed figure is very accurate give or take 1 mpg

Thanks

 

[geraldrobins]

Mine is within 6% at 56mpg and withing 1% at 50 mpg. But I expect they all vary anyway.
Best do you own check and record your fuel useage.

 

[Red C220]

Ours is generally about 10% optimistic. I monitor real mpg on Fuelly (see sig below) and always compare to the OBC reading.

10% less than the dash reads is about normal.

 

[tali]

I had a OBC on my 1999 Mondeo - that was 99.9% accurate.

 

[Benplym]

My old x5 would state 44mpg motorway average but be 33 and 35 city driving but really never achieved more than 16!! Bm's are horrendous, my pal has a tuned 300 bhp 330d and swears it's doing 50 city driving, lol.

My ml and my a6 are never more than 1mpg out and I've checked a few times

 

[paterson12]

My old x5 would state 44mpg motorway average but be 33 and 35 city driving but really never achieved more than 16!! Bm's are horrendous, my pal has a tuned 300 bhp 330d and swears it's doing 50 city driving, lol.

My ml and my a6 are never more than 1mpg out and I've checked a few times

Very true. My 2012 X6 states 38 average, never seen over 29. Most accurate car was my Alfa Romeo which actually did more than the stated figures (when it worked).