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Real MPG: the least economical cars revealed
What Car?'s laboratory tests use a real-world driving route to show what fuel economy you can really expect. But what are the worst performing cars we've ever tested?
Eleanor Cooper
Updated: 1 December 2024
Filling up with fuel can really put a dent in your bank account, so if you’re thinking of buying a new car, it’s worth knowing which ones to avoid if you don’t want to make a lot of trips to the petrol station.
On top of that, the official mpg figures you see printed in sales brochures don’t always reflect what a car will actually achieve in real-world conditions.
That’s why we conduct our own Real MPG tests, which reveal what your car can really do without resorting to any unrealistically slow acceleration or ‘hypermiling’ techniques.
Here, we list the 10 cars which performed worst in our tests and will have you stopping to fill up most often.
How we test for a car’s Real MPG
We carry out our Real MPG testing in laboratory conditions, and the cars undertake a real-world-inspired driving route using a rolling road that comprises urban, motorway and country driving. This ensures that no uncontrollable variables, such as weather or traffic conditions, will affect the accuracy of our results.
Each car is weighed and we make sure its tyres are inflated to the manufacturer’s recommended levels. Climate control is set to 21 degrees, or if the car has manual air conditioning, the temperature dial is set to the midway point and the fan speed to its lowest setting. All other electrical equipment is switched off.
The Real MPG results are calculated using the average data from an exhaust connection, which measures the car’s emissions at every second.
Read more: How we test a car’s Real MPG
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Audi S8
Driving
Interior
Practicality
Buying & Owning
Strengths
- Savage straight-line pace
- Comfortable and incredibly refined
- Plush interior
Weaknesses
- Not the most agile performance car
- Muted engine note won’t appeal to all
- Fiddly infotainment system
The least fuel-efficient car
WLTP MPG 24.6mpg | Real MPG Average 21.7mpg | Town 13.5mpg | Motorway 23.8mpg | Rural 27.6mpg
There’s a lot to like about the Audi S8 – it’s comfortable and plush, and its 4.0-litre V8 engine delivers almost supercar-level performance. But all these thrills come at a price, and that’s because it’ll have you stopping to fill up with fuel more often than any other car we’ve tested.
Indeed, with a score of just 21.7mpg in our tests, the Audi S8 definitely shouldn’t be top of your list if efficiency is a priority. However, if you’re in the market for one in the first place, it’s not likely that running costs will be too much to worry about.
Read our full Audi S8 review
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Used Alfa Romeo Giulia Quadrifoglio 2016-present
Strengths
- Fantastic performance
- Wonderful ride and handling balance
- Great noise
Weaknesses
- Heavy thirst
- Infotainment could be better
- Brake pedal feels numb
Real MPG Average 23.5mpg | Town 15.1mpg | Motorway 25.4mpg | Rural 29.5mpg
The Alfa Romeo Giulia Quadrifoglio is powerful enough to don the Italian brand’s four-leaf clover motif, which is reserved for its most potent models, so it makes sense that its engine guzzles a hefty amount of fuel.
Much like some other models on this list, the Giulia Quadrifoglio is designed for performance rather than frugality, and it does its job so well that we named it our What Car? Performance Car of the Year back in 2023.
Read our full Alfa Romeo Giulia Quadrifoglio review
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Ford Ranger
Driving
Interior
Practicality
Buying & Owning
Strengths
- Big cargo bay with a high payload capacity
- Space for four six-footers in Double Cab versions
- Good to drive for a pick-up
Weaknesses
- Not the cheapest pick-up
- Warranty could be better
WLTP MPG 20.5mpg | Real MPG Average 24.0mpg | Town 16.0mpg | Motorway 24.1mpg | Rural 32.2mpg
While the Ford Ranger Raptor sits on the podium as one of the worst performing cars when it comes to efficiency, it actually outscored its official WLTP economy results in our testing. It’s also the only pick-up on our list, and predictably its 3.0-litre V6 engine is exceedingly thirsty.
The 2.5-tonne weight of the Raptor means it doesn’t handle quite like the other sporty performance cars on this list, but it excels off-road, with its hardcore 4x4 setup giving it that go-anywhere feel.
Read our full Ford Ranger Raptor review
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Best price from £38,744
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RRP from: £38,744
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From £38,388
Lexus LC Convertible
Driving
Interior
Practicality
Buying & Owning
Strengths
- Amazing V8 sound
- Beautifully made interior
- Sporty but still comfortable and quiet
Weaknesses
- Awful usability of the infotainment system
- Tiny rear seats and boot
- A Porsche 911 is a better driver’s car
WLTP MPG 24.1mpg | Real MPG Average 24.2mpg | Town 14.4mpg | Motorway 26.6mpg | Rural 32.0mpg
Where the Lexus LC500 Cabriolet is generous with thrills, it isn’t nearly as kind with efficiency, returning an average of just 24.2mpg in our tests. That being said, it’s hard to expect a car with such gutsy performance to also be gentle with fuel consumption.
If you’re a fan of the roar of a big petrol engine, then the LC500 won’t disappoint – it’s even more booming than that of the rival BMW 8 Series Convertible and Mercedes-AMG SL, but it also settles into comfortable quiet at high speeds.
Read our full Lexus LC review
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Audi SQ5
Best buy: 2.0 TFSI S line S Tronic quattro Euro 6 (s/s) 5dr
0-62 mph: 7.2 sec
MPG/range: 39.2 mpg
C02 emissions: 163 g/km
Seats: 5
Boot: 520 litres
Insurance group: 38E
Driving
Interior
Practicality
Buying & Owning
Strengths
- Strong performance
- Supple yet controlled ride
- Lots of space for four people
Weaknesses
- Some rivals are more fun
- Inconsistent brake response
- Interior is more flash than plush
Real MPG Average 24.6mpg | Town 17.8mpg | Motorway 24.1mpg | Rural 31.7mpg
The Audi SQ5 is a sports SUV, so by nature it’s not particularly efficient, although this all changed when Audi decided to ditch the petrol engine for a rather unconventional diesel. The latest SQ5 is also now helped out by mild-hybrid power, which is sure to keep running costs low – or, at least, lower than before.
The SQ5 also benefits from a beautifully built interior, with plenty of space for front passengers to stretch out, and a comfortable ride. It’s not quite as entertaining as the rival Porsche Macan, though.
Read our full Audi SQ5 review
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Best price from £44,499
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The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £44,499
RRP from: £52,360
Nearly new deals
From £39,490
Leasing deals
From £608
About our price indicator
What Car? indicative Personal lease example (subject to status)
Audi SQ5
Expected annual mileage 5000 Term months 24 Deposit months 12 Monthly payment £607.76 Initial payment £7,293.12
Step-by-step
Leasing works a bit like a long-term rental. You drive it, but you don’t own it.
- Choose your car, pick your terms and apply for lease credit online
- Pay monthly rental payments for your chosen term length
- Drive it, enjoy it, then give it back at the end
What you get
When you lease with Autotrader you get all of this:
- Full manufacturer’s warranty
- Road tax and roadside assistance included
- Free returns within 30 days*
Excess mileage charges and return conditions apply. Subject to availability and credit status. 18+ T&Cs apply.
In partnership with
£7,538 total upfront (£7,293 initial rental plus £245 processing fee) | 5000 miles | 24 months
- Lower total monthly cost than PCP/HP
- No balloon payments
- Road tax included
Used Mercedes S-Class Cabriolet 2016-2020
Strengths
- Immensely refined
- Wonderfully comfortable
- Handles well
Weaknesses
- Expensive to run
Real MPG Average 24.6mpg | Town 14.6mpg | Motorway 27.5mpg | Rural 34.8mpg
Up until it was discontinued in 2020, the S-Class Cabriolet was one of the most luxurious convertibles on the market, and a pretty expensive one at that. Combined with its low efficiency, you’d definitely need to have deep pockets to own one.
With an immensely refined and comfortable ride, it’s no wonder the S500 Cabriolet is a five-star car in our books. It also trumps rivals like the sporty Aston Martin DB11 Volante in both handling and interior space.
Read our full used Mercedes S-Class Cabriolet review
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Mercedes GLC
Best buy: GLC250 85kWh Sport Auto2 5dr
0-62 mph: 5.9 sec
Range: 389 miles
Seats: 5
Boot: 520 litres
Insurance group: 50E
Driving
Interior
Practicality
Buying & Owning
Strengths
- Well equipped
- Plug-in hybrid has impressive electric range
- Spacious interior
Weaknesses
- Slightly firmer ride than rivals
- Stylish interior doesn't feel the most sturdy
- Petrol engines need working hard
Real MPG Average 25.3mpg | Town 18.1mpg | Motorway 24.6mpg | Rural 32.8mpg
The GLC 43 is a fast, well-equipped and practical family SUV, but it’s certainly not cheap to run. Still, if you like the sound of a strong engine, then the GLC 43 might be the car for you, since its piercing V6 engine becomes quite vocal when you work it hard.
However, it’s also available with hybrid power, which should ease the pressure on your wallet a bit. With plenty of space for four occupants and lots of room for storage, it’s a perfectly practical choice for a family.
Read our full Mercedes GLC review
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Best price from £55,495
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The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £54,495
RRP from: £55,495
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From £40,598
Porsche Macan
Best buy: 2.9T V6 GTS PDK 4WD Euro 6 (s/s) 5dr
0-62 mph: 4.3 sec
MPG/range: 25.2 mpg
C02 emissions: 254 g/km
Seats: 5
Boot: 488 litres
Insurance group: 47E
Reliability
Safety
Costs
Quality
Performance
Strengths
- Performance ranges from punchy to rapid
- More rewarding to drive than most other SUVs
- High-quality interior
Weaknesses
- Some rivals are more spacious
- Important safety kit optional
- Rivals are quieter on the motorway
Real MPG Average 25.3mpg | Town 17.3mpg | Motorway 25.1mpg | Rural 33.2mpg
The Porsche Macan Turbo returned the exact same average score in our Real MPG testing, although latest editions of the Macan come with a new engine, which performs slightly better in terms of sheer efficiency.
For those who like the idea of a high-performance SUV, the Macan doesn’t disappoint, with punchy engines and a rewarding drive that’s surprisingly agile for something of its size. It’s not the most practical, though, with some rivals such as the Audi Q5 offering a larger boot.
Read our full Porsche Macan review
New car deals
Best price from £60,245
What is What Car? best price?
The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £60,245
RRP from: £60,905
Nearly new deals
From £56,950
Leasing deals
From £733
About our price indicator
What Car? indicative Personal lease example (subject to status)
Porsche Macan
Expected annual mileage 5000 Term months 60 Deposit months 12 Monthly payment £732.87 Initial payment £8,794.44
Step-by-step
Leasing works a bit like a long-term rental. You drive it, but you don’t own it.
- Choose your car, pick your terms and apply for lease credit online
- Pay monthly rental payments for your chosen term length
- Drive it, enjoy it, then give it back at the end
What you get
When you lease with Autotrader you get all of this:
- Full manufacturer’s warranty
- Road tax and roadside assistance included
- Free returns within 30 days*
Excess mileage charges and return conditions apply. Subject to availability and credit status. 18+ T&Cs apply.
In partnership with
£9,039 total upfront (£8,794 initial rental plus £245 processing fee) | 5000 miles | 60 months
- Lower total monthly cost than PCP/HP
- No balloon payments
- Road tax included
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Land Rover Discovery
Best buy: 3.0 D350 MHEV S Auto 4WD Euro 6 (s/s) 5dr
0-62 mph: 6.3 sec
MPG/range: 34.4 mpg
C02 emissions: 215 g/km
Seats: 7
Boot: 172 litres
Insurance group:
Reliability
Safety
Costs
Quality
Performance
Strengths
- Brilliant off road
- Roomy third-row seats
- Smooth, powerful diesel engine
Weaknesses
- Interior quality is nothing special
- Wallowy handling
- Poor reliability
Real MPG Average 26.3mpg | Town 20.3mpg | Motorway 25.3mpg | Rural 32.6mpg
As a large, luxurious SUV, it’s no surprise that the Land Rover Discovery gulps down a lot of fuel, but even by class standards, its measly average score of 26.3mpg will have you stopping for fuel more often than you’d maybe like.
On top of that, the Discovery scored pretty dismally in our 2024 What Car? Reliability Survey, finishing in ninth position out of twelve seven-seaters rated, with Land Rover as a brand finishing 27th out of the 31 manufacturers ranked, so if efficiency and reliability are two main priorities, the Discovery is probably one to avoid.
Read our full Land Rover Discovery review
New car deals
Best price from £64,701
What is What Car? best price?
The What Car? best price shows you the cheapest way to buy your new car, whether it's by choosing an in-stock car through our partner Autotrader or placing a factory order.
Available now from: £64,701
RRP from: £69,540
Nearly new deals
From £54,950
Leasing deals
From £931
About our price indicator
What Car? indicative Personal lease example (subject to status)
Land Rover Discovery
Expected annual mileage 5000 Term months 48 Deposit months 12 Monthly payment £931.27 Initial payment £11,175.24
Step-by-step
Leasing works a bit like a long-term rental. You drive it, but you don’t own it.
- Choose your car, pick your terms and apply for lease credit online
- Pay monthly rental payments for your chosen term length
- Drive it, enjoy it, then give it back at the end
What you get
When you lease with Autotrader you get all of this:
- Full manufacturer’s warranty
- Road tax and roadside assistance included
- Free returns within 30 days*
Excess mileage charges and return conditions apply. Subject to availability and credit status. 18+ T&Cs apply.
In partnership with
£11,420 total upfront (£11,175 initial rental plus £245 processing fee) | 5000 miles | 48 months
- Lower total monthly cost than PCP/HP
- No balloon payments
- Road tax included
Used Mercedes S-Class 2014-2020
Strengths
- Exceptional comfort on long journeys
- Advanced technology and features throughout
- Impressive performance from all engine options
Weaknesses
- Diesel isn't as efficient as some rivals
- Expensive to maintain with high servicing costs
- Depreciation may limit resale value
Real MPG Average 26.9mpg | Town 18.3mpg | Motorway 27.4mpg | Rural 34.6mpg
Despite being helped by hybrid power, this version of the Mercedes S-Class is anything but frugal. While it offers an extremely relaxing and refined drive, this comes at a pretty high price, having returned an average of just 26.9mpg in our tests.
Despite this, the S-Class has long been considered one of the best luxury saloons around, with precise steering, plenty of standard kit and an abundance of space both up front and in the back. A new version has since gone on sale, though.
Read our full used Mercedes S-Class review
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