Under stating mpg, should I worry?

[Dolmen]

When playing around with the centre console I discovered a menu for mpg. It had not been reset for 20k miles and that would have been when I bought the van nearly two years ago. The reading was 27.1mpg. This seemed strange as the van, a 140hp 9 speed auto on lightweight van, appeared to be ever so frugal. Whilst I subscribe to the 'when the gauge is low put more diesel in, end of worry' I was determined to check it. I had a near 2000 mile trip coming up over 6 days so would get a few fill ups and a good chance to check before I lost interest. The trip computer read 28 mpg, a careful fill to fill over the entire journey showed 34.4 mpg which instinctively felt about right as well and what you would expect from a 2022 lightweight (3300kg) van. Whilst I still have to put diesel in whatever, my concern is it just a calibration issue or a symptom of something else that I should worry about?

 

[B+W vanman]

When playing around with the centre console I discovered a menu for mpg. It had not been reset for 20k miles and that would have been when I bought the van nearly two years ago. The reading was 27.1mpg. This seemed strange as the van, a 140hp 9 speed auto on lightweight van, appeared to be ever so frugal. Whilst I subscribe to the 'when the gauge is low put more diesel in, end of worry' I was determined to check it. I had a near 2000 mile trip coming up over 6 days so would get a few fill ups and a good chance to check before I lost interest. The trip computer read 28 mpg, a careful fill to fill over the entire journey showed 34.4 mpg which instinctively felt about right as well and what you would expect from a 2022 lightweight (3300kg) van. Whilst I still have to put diesel in whatever, my concern is it just a calibration issue or a symptom of something else that I should worry about?

On-board computer based mpg figures are notoriously inaccurate
But please don’t stop worrying, the rest of us don’t want the sky falling down on us………

 

[Diabalo]

My onboard mpg reading is always over to what I'm actually getting. I use the Fuelio App to keep track of my mpg.

 

[Whippet93]

Whether you are doing 28 or 35 mgp you still need to fill up. Easy enough to do a rough calculation at each fill up to get a better figure.

 

[Dolmen]

Whether you are doing 28 or 35 mgp you still need to fill up. Easy enough to do a rough calculation at each fill up to get a better figure.

It’s a pain, won’t be doing it again, I was just puzzled why the trip computer was reading so low and whether it was a symptom of something else wrong.

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[Dolmen]

But please don’t stop worrying, the rest of us don’t want the sky falling down on us………

I can do that for you if it is worrying you that much

 

[B+W vanman]

I can do that for you if it is worrying you that much

Carefree people the world over need you!

 

[Carpmart]

1st world problems eh! I’d be happy with 18mpg with my old bus!

 

[Wh05apk]

In the 4 vans we've had the display and actual figures have always been quite close once I got the hang of consistent filling with diesel, it is tempting to keep going after the first click and brim, but that can be an extra 3-4 lts, which over 70 or so lts can make quite a difference, so I always now stop at the first click, and since then the figures have always been within 1/2 mpg.

 

[rod_vw]

There is always the other variable, how accurate is your odometer? I know it won't give the difference that you are looking at but that figure has to be factored in when calculating the correct MPG figures. I did my best to check ours against a number motorway 1km marking posts and found that ours was 7% optimistic for speed so I assume the same for miles.

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[Just smiffy]

If the van was new it uses more, when it’s run in the mpg improves….

 

[BikerGraham]

The gauge drops to a quarter tank and it gets refilled. That’s as much as I know and care really.

MPG varies dramatically based on the road , style of driving and weather.

I inadvertently noticed a while ago in my car on a run that on a wet and windy day I was only getting 32-35 mpg where as normally I would get 45 plus and in good warm wind free weather around 53 mpg.

So fill up and drive then refill when the gauge drops to the level you prefer to refuel at.