Eco-driving advice

Get more out of the fuel you buy

Eco-driving advice

Save money with our eco-driving advice

Fuel consumption has a lot to do with the car you buy, but whatever you drive there are things you can do to save money and reduce energy use, CO2 emissions and pollution.

These eco-driving tips are the motoring equivalent of insulating the hot water tank, fitting low-energy bulbs and not leaving the television on standby.

They are simple ideas that really will make a difference.

Save more than 10% on fuel

When 50 AA employees took part in an eco-driving experiment with Auto Express magazine they saved an average 10% on their weekly fuel bills, with the best achieving an incredible 33% saving.

Each drove normally for the first week and then applied our advice (below) to see how much they could save in the second week...

Maintenance

  • Servicing: get the car serviced regularly (according to the manufacturer's schedule) to maintain engine efficiency
  • Engine oil: make sure you use the right specification of engine oil (check the handbook)
  • Tyres: check tyre pressures regularly and before long journeys; under-inflated tyres create more rolling resistance and so use more fuel (check the handbook and increase pressures for heavier loads as recommended)

Before you go

  • Lose weight: extra weight means extra fuel so if there's anything in the boot you don't need on the journey take it out
  • Streamline: roof-racks and boxes add wind resistance and so increase fuel consumption. If you don't need it take it off – if you do, pack carefully to reduce drag
  • Leave promptly: don't start the engine until you're ready to go as idling wastes fuel and the engine warms up more quickly when you're moving; in the winter, scrape ice rather than leave the car idling to warm up
  • Don't get lost: plan unfamiliar journeys to reduce the risk of getting lost and check the traffic news before you leave
  • Combine short trips: cold starts use more fuel so it pays to combine errands such as buying the paper, dropping off the recycling, or collecting the kids
  • Consider alternatives: if it's a short journey (a couple of miles or so) could you walk or cycle rather than taking the car? 

En route

  • Easy does it: drive smoothly, accelerate gently and read the road ahead to avoid unnecessary braking
  • Decelerate smoothly: when you have to slow down or to stop, decelerate smoothly by releasing the accelerator in time, leaving the car in gear
  • Rolling: if you can keep the car moving all the time, so much the better; stopping then starting again uses more fuel than rolling
  • Change up earlier: don't labour the engine but try changing up at an engine speed of around 2,000 rpm in a diesel car or around 2,500 rpm in a petrol car. This can make such a difference that all cars in the future are likely to be fitted with a 'Gear Shift indicator' light to show the most efficient gear change points.
  • Cut down on the air-con: air-conditioning increases fuel consumption at low speeds, but at higher speeds the effects are less noticeable. So if it's a hot day open the windows around town and save the air conditioning for high speed driving. Don't leave air-con on all the time but aim to run it at least once a week throughout the year to maintain the system in good condition.
  • Turn it off: electrical loads increase fuel consumption, so turn off your heated rear windscreen, demister blowers and headlights, when you don't need them
  • Stick to speed limits: the faster you go the greater the fuel consumption and pollution. Driving at 70mph uses up to 9% more fuel than at 60mph and up to 15% more than at 50mph. Cruising at 80mph can use up to 25% more fuel than at 70mph.

Is it best to idle or switch off?

You might be tempted to switch off the engine evey time you stop, after all many cars now have automatic stop-start systems that do just that, but is switching off manually the best thing for your wallet or the environment?

Automatic stop-start systems have several important features:

  • They have up-rated batteries, starters and charging systems, and are able to re-start the engine much faster and more frequently than a conventional starter. 
  • They may be configured not to turn off the engine if it’s cold or if head lights and other high current electrical loads are on because of the additional spike in battery charging requirement that these cause on re-start. 
  • They won't turn off the engine if the battery voltage or charge is too low 
  • They won't turn off the indicators or the radio and may maintain some heating/ventilation fan operation when off. 

As a general guide, for a warm car in daylight conditions in mild weather, turning the engine off for a wait of around a minute or more will probably save fuel/CO2 – assuming it’s safe to be without indicators and you can live with the interruption to the radio and heating/ventilation system.

A cold engine, cold weather, or additional electrical loads will all extend the period you’d have to be stationary to get a benefit from switching off.

Diesel vehicles should not be turned off during DPF regeneration as failed DPF regenerations causes oil dilution and blocked DPFs.

Coasting

Although it used to be quite a common practice to save fuel, rolling downhill or approaching a junction with the car out of gear is inadvisable because the driver doesn't have full control of the vehicle

  • You lose the ability to suddenly accelerate out of tricky situations.
  • You lose engine braking which risks brake fade on downhill stretches – overheated brakes require harder pedal pressures to stop the vehicle.

With changes in vehicle fuel systems coasting won't save you fuel these days either.

  • Old car with a carburettor – take your foot off the accelerator pedal with the car in gear and fuel is still drawn through into the engine. Fuel savings could be made by coasting out of gear.
  • Modern car with electronic engine management – fuel and ignition systems are effectively combined and controlled by one Electronic Control Unit (ECU). Take your foot off the accelerator and the ECU cuts the fuel supply to the injectors anyway so there's nothing to be gained by coasting.
  • Modern diesel engines also have the ability to shut off the fuel when you take your foot off the accelerator.

How much can you save?

Why not see how much you can improve on your current average fuel consumption or the 'official', manufacturer's figure by following our advice?

If your car has an onboard computer that records fuel economy (miles per gallon / MPG), take a note of the overall average fuel consumption you're getting now and then see how much you can improve it by. It should be possible to reset the computer so it starts recording a new average MPG.

With no onboard computer, you'll first need to find out the official, manufacturer quoted fuel consumption for your car (it's the official 'combined' figure that you want) or establish a baseline average fuel consumption for your current driving style using the steps below.

Check official fuel consumption data here >>

Measuring fuel consumption

Calculate average fuel consumption over any period by following these steps:

  1. Fill the tank and record the mileage
  2. Keep a record of any subsequent fuel purchases (you don't have to completely fill the tank again until you're ready to work out your mpg.)
  3. Ideally go back to the same pump at the same garage you first filled the car and fill the tank again to the same level
  4. Now divide the total mileage since the first fill by the total number of litres used and then multiply by 4.546 to get miles per gallon (for example if you've covered 1000 miles and used 101 litres of fuel, your average mpg = (1000/101)x4.546 = 45mpg)

(9 October 2014)