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How do I get better fuel economy?

Hi there,

I bought the new Opel Astra in January, a diesel 1.7L CDTi with 110hp. The car is well run-in at this stage with over 4,000km on the clock. I am only getting about 42mpg; the tank holds 56 litres and I am lucky to get 800km from this. The dealer has told me that it should be closer to 55mpg. I have a provisional appointment made with the dealer for him to do an emissions check on the car. Can you think of what might be causing the poor mileage considering I am not a hard driver and do obey the speed limit?

Carl Cody (Kilkenny)

May 2010 Filed under: fuel economy and emissions

Expert answer

Hi Carl,

The thing about fuel economy figures from the manufacturer is that they are often very difficult to match. We seldom match them, as they are recorded using specific lab conditions and are often not really reflective of real-world conditions.

There are some things you can do to improve your fuel economy however:

1 Pump up to cut down 

Under-inflated tyres create more resistance. That means your engine has to work harder, so more fuel is used. Check and adjust your tyre pressures regularly, and also before long journeys.

2 Less clutter means less CO2 

Clutter in your boot is extra weight in your car. By removing it, you could reduce your engine's workload. This will burn less fuel.

3 Drive at an appropriate speed 

Staying at or within the speed limit not only increases driver safety, it also reduces fuel consumption. At 110km/h you could be using nine percent more fuel than at 100km/h, and up to 15 percent more fuel than at 80km/h.

4 Less stopping and starting 

Every time you stop then start again in a traffic queue the engine uses more fuel. Keep an eye on the traffic ahead and slow down early by gently lifting your foot off the accelerator while keeping the car in gear. The traffic may have started moving again by the time you reach the vehicle in front, so you can change up a gear and be on your way.

5 Over-revving accelerates emissions 

Modern car engines are designed to be efficient from the moment they are switched on, so revving up like a Formula 1 car in pole position only wastes fuel and increases engine wear. Using your gears wisely by changing up a gear a little earlier can also reduce revs.

6 Idling is wasting fuel 

When the engine is idling, you're wasting fuel. If you're likely to be at a standstill for more than three minutes, simply switch off the engine.

 – Source: Defra UK

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