It would be easy, or so I thought. But getting a ton out of this car on public roads was proving really difficult. My chosen 12-mile (19.3km) circular route flowed along country lanes with few other drivers about. Jam sandwiches rarely ventured along here, which is just as well because any police officer would suspect I was drunk by driving in such a manner. But perseverance began to pay off. The digital display on the dashboard was creeping higher: 70, 80 and 90 in places. Then, after several laps, it turned from 99 to 100 and more. But sustaining that performance over more than a mile was impossible.
The reason for this escapade was to address the complaint that crops up whenever motoring is discussed: you can't get anything like the miles per gallon from a car that the manufacturer claims. The reason is that the official figures come from a European test procedure, carried out in laboratory conditions with the car on a rolling road. It is a consistent way of measuring things, but it bears no relation to real life.
What I wanted to discover was not just what it took to match the official consumption of one of the most fuel-efficient cars on the market, but if I could beat it. My target was a real average consumption of 100mpg (2.8 litres per 100km). If that is possible, then the age of everyday ton-up cars cannot be far away.
My chosen car, a Volkswagen Polo BlueMotion, has all the credentials of a fuel miser. It is full of economy features, including a 1.2-litre diesel engine that has three cylinders to burn fuel instead of the usual four, long gear ratios to reduce engine speed and a stop-start system to switch the engine off if you have to wait at junctions or in queues.
The figures for this car are impressive. The European fuel-economy test consists of two parts: an urban cycle in which the car goes through a set procedure of accelerating, cruising, slowing and idling that is supposed to represent driving in town, and an extra-urban cycle to mimic main roads. A combined fuel consumption is calculated from an average of the two, weighted for distance. The Polo BlueMotion has a stated urban figure of 67.3mpg, an extra-urban one of 91.1mpg and a combined 80.7mpg. So wringing a ton out of this car should have been a piece of cake.
It wasn't. Even getting close to those figures required tedious hypermiling techniques, like feathering the throttle to eke out the fuel, avoiding any braking so as not to lose momentum and constantly changing gear to maximise the engine output. One hypermiling trick is to give the accelerator a blip, take your foot off and glide. This pulse-and-glide technique can save a lot of fuel, but your speed might dwindle to walking pace as you crest a hill. It is a horrible way to drive and will send anyone following you bananas.
Even doing all these things I could hold the fuel consumption above 100mpg for only a short spell. But at least it was possible. After several complete laps the best average consumption was a tad under 80mpg. Driving normally in town and country the car returned an average of 58mpg. Compared with many cars that is very good, but it is well short of what the book says.
As a town car, the Polo BlueMotion would be an economical runabout (it qualifies in Britain for zero road tax because of its low CO2 output). But not for me. I had to rev hard to drive off from junctions at a speed I felt comfortable with, especially in traffic. A regular Polo is nicer to drive, and with a petrol engine instead of a diesel is several thousand pounds cheaper.
Diesel engines are more economical and so emit less carbon dioxide than petrol engines, but they might not be the best choice for frugal motoring—even though about half the cars sold in Britain are now diesels. Diesel has become more expensive than petrol, and diesel-engined cars are more costly to buy and repair than petrol cars. That may mean having to travel more than 15,000 miles a year in a diesel to be any better off during a typical three years of ownership. Moreover, new emission regulations mean modern diesels are not suitable for making lots of short journeys, because their exhaust filters need plenty of long trips to prevent them from clogging up.
Most carmakers now offer a range of both petrol and diesel models with added fuel-saving abilities. Some, like the Polo BlueMotion, use fewer cylinders: Fiat's TwinAir range have two cylinders and Ford's new small Ecoboost engines have three. These engines might be tiny, but they are far from gutless: the one-litre Ecoboost engine in a Ford Focus produces the same amount of power as a four-cylinder two-litre engine did in a 12-year-old Focus. But some engines may deliver that power through wide fuel-saving gear ratios, so only a spell behind the wheel will reveal if that suits your driving style.
Many of these frugal motors come with a saving-the-planet badge attached and that, of course, might mean paying more. BMW uses EfficientDynamics, Vauxhall has ecoFLEX, Mercedes-Benz uses Blue-Efficiency and Hyundai badges its economical cars as Blue Drive (in eco marketing, blue is the new green). It pays to compare them with the standard model, which could be cheaper, drives better and still returns a good fuel economy.
But how will you know if the official figures are unreliable? It is becoming easier to find out real-world fuel consumption. Various motoring websites and magazines are compiling such data from users. But fuel-economy metres in cars may not be accurate either. What Car? magazine is now using sophisticated measuring gear to establish true mpg figures for all new cars. Some get close to their official figures, but others are way off the mark (see below).
With so many engineers beavering away on making cars go farther with whatever fuel is in their tanks, we should, within a few years, see the first 100mpg cars. On paper, that is, unless governments come up with a realistic way to measure fuel economy.
*Government combined figures/What Car? test results
BMW 320d Sport
Beamer with less thirst than some small cars.
Ford Focus 1.6T 150 Ecoboost
A hatchback that is nice to drive.
Mini Cooper 1.6D
Fun for the fashion-conscious.
Toyota Prius 1.8 VVT-i T Spirit
Older hybrid, but not so green.
Volkswagen up! 1.0 black
New small car, at home in the city.