2010 V60 - trip computer: imprecise fuel economy shown
 

I have recently purchased a V60 manufactured in 2010 December. The vehicle was a demo car at a Volvo saloon, almost brand new with less than 800 miles in its odometer.

As I'm driving in Europe with expensive diesel :-) I always take care of fuel economy and therefore I keep watching the average fuel consumption.

I reset the counter as I had a full tank and when I needed to refuel I calculated the real consumption and checked the result with the avg consumption shown by the trip computer.

I was quite surprised that there is almost 10% difference between the real consumption and the measured consumption values.
And of course the real consumption is 10% higher than the value shown in the trip computer.

Does anyone know why the measurement is so imprecise?
It's a bit frustrating given that I expect an almost perfect vehicle in this category ...

Many thanks!

I asked the repair station where I got the information that I should not rely on this gauge. This will never be precise as it is not calculated for the full amount of fuel and mileage between 2 resets rather it is calculated based on the last X miles.
This seems to be a bit misleading/wrong approach to me - before I had a VW Passat where the average consumption gauge was perfectly precise.

Given that the engine controller computer needs to be very very precise I think calculating an average consumption should not be an issue.

Any thoughts?

when you calculate the fuel you divide gallons by miles your working with the fuel
the car can't measure how much fuel passes through the fuel rail so it uses the readings of how much air passes through the MAF sensor and calculates fuel usage based on how high the air fuel ratio is verses how much air passes through the MAF
its good but not 100% quite clever in my opinion.

Thanks for your answer!

Do you think this is the same with a diesel engine? I guess it is valid for petrol engines, but diesel does not work with airflow regulation rather it changes the amount of fuel injected into the chambers ... as far as I know ...

My VW provided a fairly precise measurement with the trip computer. It was also a diesel engine.

well all car companies are a little different, that's how Volvo calculates the average mpg on both petrol and diesel to my knowledge. I have to say though I don't know nearly as much about diesel engines as I do petrol ones, or even electric for that matter lol.

I had a chat on this with the technical support guy at the Volvo station where I bought the car.
He stated that the computer measures the fuel line pressure and the injector open time window (when the diesel fuel injection is happening) and calculates the consumption based on these.
He told me that there could be differences caused e.g. by the environment temperature, causing the fuel to expand and take more place for the same amount.
He stated that as we have a very hot summer now, it will be more precise when the weather will be more average ...

For me it seems to be a bit of "don't bother with it, just leave it as it is" approach.
But I will keep checking the measured values against the data shown by the computer.

Thanks,
Balazs