How accurate is your dash computer?

[MBDevotee]

Just bought a New (to me) CLK.

Got a few things that need sorting on it - which I'll post in the relevant sections.

Photos to follow once I have sorted a few minor cosmetics on it (missing wheel badges etc).

HOWEVER - I have now just used up the first tank of fuel bringing it home and a bit of running around. The fuel consumption on the dash showed the car had done 44.7 mpg from reset until I topped up.

However working it out, I did 456.7 miles and put in exactly 55 litres of fuel. I brimmed the tank absolutely to the lip at the start and end.

Now I realise that on one tankful you can't tell too much - however working it out, that makes it just 37.7mpg.

I'd expect 1 or 2mpg difference - but nearly 20% over-estimate from the dash??? That seems excessive to me.

I'll keep an eye on it - but just wondered, how accurate are the merc computers for telling you the MPG and other stats?

Done a poll to see how accurate yours is - please only complete if you actually measure your MPG accurately.

Thanks

 

[turbopete]

ive found that with my c class, i can fill it to the brim, but it sometimes will drop back so im not convinced the brim to brim method works if taken literally.

due to unemployment, i have no choice to run my car near empty all the time. i put between £20 and £30 of diesel in per fortnight and travel between 130 and 200 miles approx per fortnight (depending on what i need to use the car for) which makes its lifetime average since ive had the car of 47.something mpg (cant remember the exact figure) as near correct as makes a difference to me. diesel here is 135.9ppl at the moment, which equates to me using around 3-4.5 gallons per fortnight, depending on the runs i need to do.

 

[S.Speed]

On both my C classes the cars computer has been amazingly accurate..
I would say the pre face lift was slightly more accurate but i am nit picking now..

 

[MBDevotee]

Mine is consistently lying....

I am always being told it's hovering around 44 - 44.3 however I am averaging 37 ish (37.3 - 37.5) no-where near 40!

 

[rf065]

Can you be sure it has not been remapped?

Mine consistantly gets 1 or 2 MPG more than the dash display states.

Russ

 

[Alex M Grieve]

On several cars (C 220 CDI, S 320 CDI, R Class 320 CDI) the trip computer has been correct to <0.5 mpg.

I keep records of all the fuel I put in, over tens of thousands of miles, so I am confident of the data.

I see the OBC has a clue to current performance rather than an absolute answer. As you say, you will know better once you have done a couple of thousand miles.

 

[juani]

2 mpg less