Weird MPG

[SuperHans]

Hi, I have a c270 cdi which I often drive about 250 miles weekly up and down the m6. The computer readout reads between 52 and 56 mpg average which to me seems very good. However, if I work out fuel consumption the old fashioned way, tank to tank, I'm working out the consumption at being around 30mpg (£40 got me 250 miles recently).

Now I've heard of the computers being inaccurate but this is a joke!

Have you guys ever seen anything like this? Something wrong with my car?

 

[Hawkwind]

Depends on what the parameters are that the computer uses, it may not be using the figures for the whole journey, as you and I would normally expect. Therefore giving misleading readings, that will however look good to the unsuspecting.

 

[bobbob455]

The computer on my C270 usually shows an average of around 45mpg. During a recent 200 mile motorway run I got it upto 65.7 !! I have never considered the computer being incorrect, I'll check it when I next fill up against the 'old fashioned' way of working it out.

 

[sc3992]

Got this on the trip computer which turned out to be 62.7mpg tank to tank, over 2763 miles the average is 61.39 mpg. The car is a W213 2ltr 9 speed auto......

 

[John]

I've always understood computers to be optimistic (10 > 20% usually).

Brim to brim manual calculation is the only way to know for sure.