S60 Electrics: Trip Computer Accuracy - mpg

[wirralepcs]

I have always took it for granted that my trip computer readings of 50 mpg or thereabouts were accurate but a recent calculation based on diesel used between two full tanks over 523 miles came out at only 39 mpg. I am 100% certain that my calculated figure is correct and so I wonder why the computer figure is so far out. Is it based on the miles from say new ( zero miles ) until now ( 195,000+ miles ) or if not how exactly is it calculated?

My car is a 2002 S60SE D5

[Bonefishblues]

That Gen was always ridiculously optimistic, simple as that. Volvo got the hang of it in about 2010 or so. Our 2012 XC is very accurate

[Roy V70 850]

I don't take any notice of mine, it's far too generous. I too checked against what I put in the tank.

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2004 V70 D5 163bhp manual 179k miles

[BobbyDazzler66]

Originally Posted by wirralepcs

I have always took it for granted that my trip computer readings of 50 mpg or thereabouts were accurate but a recent calculation based on diesel used between two full tanks over 523 miles came out at only 39 mpg. I am 100% certain that my calculated figure is correct and so I wonder why the computer figure is so far out. Is it based on the miles from say new ( zero miles ) until now ( 195,000+ miles ) or if not how exactly is it calculated?

My car is a 2002 S60SE D5

If you are calculating this yourself, make sure you are using UK gallons and not US gallons. Your 39 vs 50mpg would be explained by using US gallons (if you converted from litres to gallons to get the fuel used).

[LIB]

I generally find my P3 D5 V70 is 10% optimistic whenever I've properly calculated it.