/ Motoring

How many miles can your car really do on a full tank?

Car fuel dial

Like many motorists you probably have a good idea of how many miles your car can do on a full tank of petrol. But do you know if it is anywhere near what the manufacturer claims?

When I bought my car, I wanted a reasonably priced vehicle, that was small and easy to park, and not too expensive to run. I chose a Peugeot 107, with an advertised 508 miles on a full tank of petrol. But after a few months I noticed I never managed to get near that – the closest I ever got was 330 miles.

Obviously I didn’t drive until the tank was completely empty so it could have done a few more miles, but that’s still quite a difference between the real and claimed figures.

New Which? research put 200 cars through the same test and found that 98% couldn’t match or beat their miles per gallon (mpg) claim. The car that performed worst compared to its official mpg figure was the Mitsubishi Outlander PHEV (a plug-in hybrid), which overstated its mpg by 120%, costing £459 a year in unexpected fuel costs.

Other studies have shown that the gap between official test results and how we drive in the real world has increased over the past years, so the problem could be getting worse. But why is this happening?

Why fuel claims aren’t accurate

The problem lies with the Europe-wide test used to measure fuel use, the New European Driving Cycle (NEDC).

The test is called ‘new’ but it was introduced in 1970 and last updated in 2007. It’s outdated and doesn’t properly measure the kind of driving we do today, for example on motorways.

It also contains a number of loopholes. Manufacturers can, for example, opt to switch off air con and lights when testing, or increase tyre pressure above recommended levels. And as there is no standard way of testing, this means that you can’t make a proper comparison between different cars.

Many of you have already told us you knew the claims were misleading. Malcom R told us in 2013: ‘EU fuel consumption figures do not represent real-life, and are not intended to.’ Vynor Hill said: ‘Manufacturers’ claims are of no use to anyone.’

It seems unfair that a product that isn’t meeting its claimed performance doesn’t suffer any consequences and consumers just have to bear the brunt of it, or do their own research.

Steering in the right direction

A new and improved fuel efficiency test that would address many of the current one’s weaknesses is due to be introduced in 2017 by the European Commission (EC). This actually closely mirrors our own test and more accurately estimates fuel use.

But some factions are trying to stall the introduction of the new test to delay it to 2020. That would be another five years of useless fuel claims.

We don’t think this is right, and are urging the EC to stick to the planned timing, so that you won’t be taken for a ride any longer.

Do you think official miles per gallon figures reflect reality? Do you agree the EC should bring in the new test by 2017?


I am pleased to see a comprehensive press release from Which? that contains both a factual explanation plus useful information. I wonder how much of this the press might use?

I’m also glad to see that Which? seems to have changed tack slightly in pointing the finger for poor real life mpgs compared with test results at the real culprit – the EU’s inadequate NEDC test regime. This is imposed on car makers. A slight pity that the opening paragraph
“Diesel emissions are not the only example of misleading claims from manufacturers. For years our testing has proved that fuel economy figures do not match official MPG claims – and VW is not the only culprit.”
still seems to direct blame at the carmakers though.

Just going to share my previous comment for the new page of comments.

We have published a new convo about the VW scandal: https://conversation.which.co.uk/motoring/volkswagen-vw-diesel-car-pollution-emissions-mpg-scandal/

And we’ve put out a press release : http://press.which.co.uk/whichpressreleases/new-fuel-efficiency-tests-needed-to-rebuild-trust/

Richard Lloyd, Which? executive director said:

“Our research has consistently showed that the official test used by carmakers is seriously in need of updating as it contains a number of loopholes that lead to unrealistic performance claims. The car industry needs to focus on how to rebuild trust with consumers and we want to see the new fuel efficiency test introduced as soon as possible.”

With a heavy Volvo estate and a D5 diesel engine my MPG varies between 35 and 44. It all depends on using your foot wisely, applying cruise control, type of road, correct tyre pressure, and the weather.. . because diesels chew more fuel when it is cold as they need longer to fully warm up. The reward for having a modern engine with an electronic DPF (dust particle filter) is an expensive replacement of the filter unit (£500 easily) which is clogged up with black coal slurry, which has been kept inside the engine system.
I do not understand why the cleanest fuel of all LPG is not more applied to the motoring world in the UK. It is perfectly clean (60-70% of the emissions output of unleaded petrol). It needs some modification to the engine, but it burns cleanly.

I have a 57 plate Mercedes E220 CDi. The Mercedes handbook says it does an average of 32.5 to 24.5 mpg. Looking at the computer readout for the last 3,700 miles it has done 37.0 mpg. From time to time I’ve checked this figure against a tank of fuel and give or take, its reasonably accurate. Most of my driving is local with occasional motorway trips so I’m quite happy with Merc’s figures for this car.

I had a Volvo XC 70 AWD for over 9 years and drove 176,000 miles; during this period my car exceeded the official figures (41 mpg) by 0.3 mpg. I now have a new and more powerful XC70 AWD and after 26,000 miles I an just below the official figure. From this I conclude Volvo figures are quite accurate.

How do you assess the real-life mpg of the Mitsubishi PHEV? If you make an assumption as to the proportion of EV versus ICE mileage what is this assumption? I drive one and most of the time I use no petrol at all so the mpg is amazing!

If you look on Honest John’s mpg website it gives an average figure for a 2.0 Outlander PHEV as 43.5, based on 19 users submissions. The “official” mpg is 148.6, which is down to the nonsensical European official test cycle which has no relevance to hybrid vehicles. Think, however, of how much energy is used to generate the electricity used to charge your vehicle – that requires gas, oil, wind or something that is not free 🙂 . Unless you have solar panels? Perhaps a couple on the roof of your car to help recharge the battery? Ford showed a concept C max like this which claimed to run 21 miles on solar power. But the consensus seems to be that solar panels will not power cars yet, but could be useful to run auxiliaries like air conditioning.

Long way to go before solar panels will power a vehicle of anything in the vehicle.
Solar PV operates around 150watts per square meter at peak sun so the surface of a car would not hold many watts
The answer is more free energy and less old wives tales about it.

I don’t understand the furore – for conventional ICE cars I’ve always used the Urban figure, as I live in a city, to provide my expectations for normal usage.
And everyone knows EVs & PHEVs are only as good as the charge they receive before use …. I’m planning a Chevrolet Volt, as only about 2% of my journeys are greater than 15 miles, and as a general rule I can ‘top off’ the batteries at destinations before returning home …….

I have two cars, an 11-year-old Golf 2L diesel which my wife uses, and a year-old Mazda 6 diesel. Both are manual. I bought the Mazda at least partly because of the claimed 70-plus mpg; after all, it’s a latest generation diesel, it must be more efficient, surely? Not so. On the same roads, same speeds, driven in the same way, the Golf consistently does 55 mpg, whereas I’m typically achieving 46 mpg in the Mazda. The only way I can get to the 70+ figure is to set the cruise control to 60 or less and drive down an empty motorway – and who does that? In mitigation, the Mazda has an extra 200cc; but we are talking claims here, are we not?
And don’t ask me about Mazda paint quality….

It seems drivers can account for a lot of the differences in what they do per gallon.

” A new study by researchers at the Department of Energy’s Oak Ridge National Laboratory has quantified the impact speeding and slamming on the brakes has on fuel economy and consumption.
They found that aggressive behavior behind the wheel can lower gas mileage in light-duty vehicles by about 10 to 40 percent in stop-and-go traffic and roughly 15 to 30 percent at highway speeds. This can equate to losing about $0.25 to $1 per gallon.
Read more at: https://phys.org/news/2017-09-gas-drivers.html#jCp