Running A Car - How to save fuel

24 May 2012

The cost of filling a car up with fuel is now as significant as that of filling a supermarket trolley with the family's weekly shop.

Fuel costs are beyond the control of individual motorists, but there are plenty of ways in which you can maximise the value of every litre you put into the tank.

The first and perhaps most obvious fuel-saving tip is to drive fewer miles. That may sound a bit pie in the sky, but the fact is that almost every motorist throws away money simply as a result of not planning journeys better.

Combine tasks and chores in one trip rather than making lots of separate ones. Optimise frequently-taken routes – especially your drive to work. Less congested roads may add a few miles to your journey, but these roads can save you money if they help you to avoid traffic black spots. If you've got a sat-nav, or even a map, use it rather than driving around aimlessly in the vague hope of finding your destination.

To move weight, your car needs energy. The more weight you have to move, the more energy the engine will have to generate, so don't burden your car with redundant stuff you don't need. Carry a snow shovel in winter, but not in summer. If the kids aren't travelling, don't take their buggy. If you're not using the carrying capacity of external kit like roof boxes or bike racks, take them off the car. The extra wind resistance these items create has a surprisingly profound effect on fuel consumption. So does drag from under-inflated tyres, open windows and sunroofs.

Choose the right car for you. The car selection process is harder than it should be because 'official' fuel consumption figures are often quite inaccurate. Real-life driving is more demanding than the EU laboratory tests which produce the official figures. You should typically expect to get 10 to 15 percent less miles from a gallon than the Government figure suggests.

That's why What Car? has launched True MPG, a real-world fuel economy test that gives you a personalised average mpg figure you really can expect to achieve on UK roads.

The biggest difference between our True MPG fuel economy tests and the official tests is that they're conducted on roads rather than in a laboratory. Our test starts with a thorough warm-up of the car, because engines are less efficient when they're cold. The route begins with urban driving at an average speed of 15mph, followed by a mix of dual carriageways and motorways at an average of 60mph, and finishing with another urban loop. Our testers drive at a steady pace, avoiding heavy acceleration and braking whenever possible.

The average fuel consumption on the test route is calculated from CO2 emissions, but because traffic volume varies, we only use this economy figure as a starting point. Sensors constantly record road speed, exhaust manifold pressure, throttle position, altitude, humidity and air pressure to produce a comprehensive data set, and what can fairly be called a car's ‘true' mpg.

Drive in a more fuel-efficient way. You don't need to be a professional driver to do this. The key words are ‘gentle', and ‘anticipate'. Accelerate and brake gently, changing up to a higher gear as soon as possible, but not so early that the engine is struggling at low revs. As a general guide, use 2000rpm as a typical diesel changeup point, and 2500rpm for a petrol car.

Be aware however that modern engines are built and tested to perform reliably at high engine speeds. Driving exclusively at low revs can build up potentially damaging residues on valves, or clog diesel particulate filters. Occasional runs up to higher revs are actually good ‘medicine' for your car's engine.

Accelerating as slowly as possible is no longer considered to be the best fuel-saving option. Apart from anything else, this technique can irritate other road users and give rise to safety considerations.

Look far ahead and keep moving by anticipating obstacles. Ease off the throttle and keeping the car flowing rather than speeding up and braking repeatedly. Drive with a pushbike mentality: build up momentum downhill to help get you uphill, and ‘read the road'.

Although it's not always practically possible, maintaining a steady 55-60mph cruise is the most fuel-efficient way to drive on motorways. Sticking to the speed limits generally is a good idea for your wallet; cruising at 70mph uses up to 25 percent less fuel than 80mph.

If you're going to be at a standstill for more than a minute, switch off the engine. Many modern cars come with automatic engine stop-start systems. These deliver good results if they're allowed to work, and are not being over-ridden by the driver.

Switching on ‘comfort features' like the stereo, rear demisters, lights, or air-conditioning adds to your fuel bill because the engine has to work harder to generate the power that they use. Air-con systems are a lot more efficient than they used to be, but they're still relatively power-hungry, so don't be tempted into leaving your car's air-con switched on. In the UK, the standard heating/ventilation system in most cars is more than up to the job of handling almost all of your climate and demisting needs.

Poorly-maintained engines will run less efficiently and use more fuel, so it makes sense to keep up the servicing regime. Reducing mechanical inertia and friction is now at the heart of most manufacturers' thinking. BMW's EfficientDynamics is a good example of how this kind of approach can result in great economy without compromising performance.

Dirty oil doesn't lubricate engine parts as well as clean oil. Changing it isn't a cheap exercise nowadays, but checking and replenishing the level will maintain the quality of the oil, especially if your engine is designed to consume a little oil in everyday use. It's the equivalent of a slow-motion oil change.

It's also a good idea to fill up from half full rather than empty, to minimise the evaporation in your tank. Pump slowly to minimise the creation of vapours that get sucked back into the garage's underground storage tank (at your expense).

See also
Reviews of the most fuel efficient cars

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