Fuel computer exaggerating?

[40t]

The fuel computer consistently over-states consumption by 6.5% to 8.5% (e.g. 38 mpg quoted is really 34.8). That's based on filling until the pump cuts off, so presumably variations in the cut-off point account for the range of results.

Does anyone else experience this degree of error? If I were to fill up to the brim, the results would perhaps be more accurate (or, at least, more consistent), but I can't see why the degree of error would be lower - unless I'm missing something?

[prc68]

I don't think I've ever had a car that didn't. 8.5% is actually pretty low.
All the VW's I've owned had more than 15% discrepancies, and even on my old c-class mercedes it was >10%

[tommyweaves]

I think that's pretty standard for all cars!

[Bonefishblues]

That's accurate compared to the previous generation, trust me!

[tt82]

Mine is generally a few MPG optimistic. My experience is the better the fuel you use, the more accurate it is.

[Tony500]

My computer says averaging about 39.9 but from my calculations I’m getting 30.2mpg

Pretty bad for a 2.0d taking it easy 😵

[Simon Jones]

The fuel gauge and average consumption are a bit bizarre in operation. I run on LPG, yet the petrol gauge will drop from about 1/4 full to zero over about 40 miles (along with the miles remaining reading) despite not a drop of petrol being consumed. As soon as ignition switched off and on, the readings revert to their previous values. On my P2 XC70, there were two tank senders (one in each side) but on the P3, VIDA only reports one sender with shows about 30 litres even when the tank is full and the gauge also reports full.

[I-S]

http://www.askisaac.com/images/volvompg2.png

Orange line = trip computer, blue line = tank-to-tank calculation.

Yes, over 4.5 years and over 40000 miles, the trip computer has almost invariably been optimistic.

[apersson850]

Originally Posted by 40t

The fuel computer consistently over-states consumption by 6.5% to 8.5% (e.g. 38 mpg quoted is really 34.8).

Which means it really under-states, doesn't it? Since miles per gallon isn't consumption, that's range. Consumption is measures as quantity per distance, like liters per kilometer, or gallons per mile in you case.

Then it's pretty normal for these cars. When my car claims I can drive, in rural areas, with a consumption less than 6 l/100 km, it's really a bit over that value instead.

My (petrol) 854 Turbo from 1994 was much more accurate than the diesel I have now. It's an automatic AWD D5 (230).

[tommyweaves]

Originally Posted by apersson850

Which means it really under-states, doesn't it? Since miles per gallon isn't consumption, that's range. Consumption is measures as quantity per distance, like liters per kilometer, or gallons per mile in you case.

Then it's pretty normal for these cars. When my car claims I can drive, in rural areas, with a consumption less than 6 l/100 km, it's really a bit over that value instead.

My (petrol) 854 Turbo from 1994 was much more accurate than the diesel I have now. It's an automatic AWD D5 (230).

I don't know anyone in the UK that refers to their economy figures in gallons per mile, or litres per kilometre. I's always miles per gallon.

I think everyone reading the OP's initial post knew that by "consumption" it was a referral to a measure of economy. Therefore the computer IS overstating.