2010 D5 Fuel Consumption Fluctuations

[Andiroid]

Hi, just wondering if anyone has any experience with fluctuations in fuel consumption as indicated by the onboard computer? I have only had the car for few months and have started to see some rather high fuel consumption readings. Up to 88l per km (I’m in Australia). I have had a full service since I have bought it and they said nothing came up in the scans. Just wondering if this is something that can be fixed and how?

Any insights would be welcome!

[xavierx]

Fuel consumption will increase significantly when the DPF is re-generating. Mine will go from about 40mpg at 60mph to 28mpg while the regen is running

[Andiroid]

Hi, yes I had read that, but this has been going on for a while now. I have had several good highway trips in that time too that they suggest doing to help with the burning off of the particle filter.

[simboc2004]

I reset my average MPG every time I fill up and I have found it sometimes miscalculates to a far worse reading. Resetting it generally gets it back to correct readings. Mine's a 2011 car, so may well be similar.

[capt jack]

Is it fair to say that car computers are notoriously unreliable when it comes to fuel consumption?

The most important figure is the one that you calculate for yourself each time you fill up.

Before worrying too much it'd make sense to do a proper calculation based on fuel bought and miles driven.

Jack

[xavierx]

Originally Posted by Andiroid

Hi, yes I had read that, but this has been going on for a while now. I have had several good highway trips in that time too that they suggest doing to help with the burning off of the particle filter.

I've not had this with my Volvo but my last diesel BMW I got a fault with a dpf pressure sensor that caused it to re-generate the DPF over and over and over, so it might be worth getting a scan done with VIDA to see if there is anything abnormal, particularly if your actual real MPG is lower than expected

[Magrathea]

I also had large fluctuations with actual fuel mileage. On of the biggest was a plug in coolbox. That dropped it from 40mpg+ to 28mpg. Also air conditioning use. On the motorway switching off the aircon would give another 10mpg at least.

[Kev0607]

Originally Posted by Andiroid

Hi, just wondering if anyone has any experience with fluctuations in fuel consumption as indicated by the onboard computer? I have only had the car for few months and have started to see some rather high fuel consumption readings. Up to 88l per km (I’m in Australia). I have had a full service since I have bought it and they said nothing came up in the scans. Just wondering if this is something that can be fixed and how?

Any insights would be welcome!

Are you sure you're looking at the average mpg reading? It will say "average" and then whatever the figure is.

I suspect you're looking at an "instantaneous" reading, which is also an option that you can look at, but it means nothing.

On the wiper stalk, turn the little wheel until you get to "average" mpg. That's the one that means the most, in a sense. The other fuel relation options you can look at are useless. Note, the average mpg isn't "that" accurate either.

Don't be surprised if the average gives a false reading in-car too, its not really accurate. As mentioned in other posts, the best way is calculate your mpg is to note down how many miles you've done (or use the trip function) against how much you put in/cost per litre. Don't rely on computers.

[Andiroid]

Hi, yes. I do mean the instantaneous reading. I only noticed the spike because when I bought the car II was very interested in what the mileage would be. For weeks the highest it got to was about 48klm per liter, like under harder acceleration from standing up a steep incline. Then one day I started noticing readings of up to 89km per liter under normal, moving with the traffic acceleration on flat surfaces. Usually, this would have been a 30-35l reading. It still fluctuates between very high and what I would say is “normal”.
The average calculation reading has gone from a consistent 8.4l per 100km to 9.9klm.

I just wonder if a fuel pump or injector issue?

[apersson850]

My D5 (230 hp/470 Nm) in an XC70 AWD automatic currently displays 7.7 l/100 km. Last time I looked at our D4 (181 hp/400 Nm), in the same kind of car, it displayed 6.9 l/100 km average consumption. But the D5 is towing much more than the other.

Looking at the instantaneous consumption, I rarely see above 50 l/100 km. That's when accelerating through gears. Towing a camping trailer, consumption is typically 11-12 l/100 km.

Around 90 l/100 km is for sure excessive, unless you try to drive in some rallye competition.