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Fuel Economy: Myth or Fact?

Wringing the most out of our fuel is very much the in thing, whether you’re a greenie or a meanie. Information about what you can do to save fuel and improve your car’s fuel economy gets handed on and handed around. But are some of the things that Uncle Fred taught you actually going to help improve your fuel economy?

• Myth or Fact? You need to warm your car up before you can drive it properly.
Myth. Even if you are in the chilliest parts of the world, you don’t need to warm a car up before you can drive it. Sure, you might need to apply the choke for a little bit in the depths of winter, but if the engine is turning over, you’ve got the energy needed to turn the wheels. If you do use the choke, remember to turn close it off after about five minutes.

• Myth or Fact? Small cars are more economical than large cars.
Myth. As my fellow-blogger David commented, fuel economy is getting very, very sexy in the motoring world, and the guys and girls who come up with car ads are just as likely to mention the fuel economy figures as they are to mention the torque. This means that fuel-saving technology is being applied to medium-sized and even large cars. This is good news of all of us for whom a little Honda Jazz  or similar is impractical – there’s no need to jam a family of leggy teenagers into the back of a little hatchback in the interest of saving fuel.

• Myth or fact? Driving less aggressively is more fuel efficient.

Fact. If you demand less of the car, it can work more efficiently. Feather-light touches on the accelerator, gentle braking and smooth cornering are easy on the car and mean that it uses less fuel. Fierce acceleration, hard braking and tight cornering might be all right on the race track but are bad for fuel economy, as well as making you obnoxious on the road to your fellow drivers. This is anecdotal evidence, but I’ve recently picked up a 4-litre Ford Fairlane . Keeping a light foot keeps the average fuel consumption (according to the trip computer) nice and low. Plant the boot and the figures soar. Think of the effortless and graceful soaring of a seagull or an eagle compared to the aggressive and frantic flapping of a chook.

• Myth or fact? After-market additives and thingummies can make your car run better.
Myth. According to a Reader’s Digest article and the US Department of Energy, most gadgets and additives that you chuck in along with your petrol don’t make your car any more efficient, and the only thing that they clean out is your wallet. The exception is a full conversion to LPG or something along those lines.

• Myth or fact? Replacing your air filter will improve your fuel economy.
Fact – sort of. Changing the air filter does indeed improve the fuel economy of older cars. However, with modern cars, changing the air filter improves the performance but doesn’t actually improve the fuel economy. This is because a lot of modern engines have computerised controls that maintain the right fuel to air ratio, no matter what state the filter’s in.

• Myth or fact? Idling uses more fuel than restarting your car.
Fact. If you have to wait for that person who’s running late or if you’re held up by road works, switching the engine right off and restarting it again uses a lot less fuel. OK, it might not be a good idea to do this at the traffic lights, unless you know that you’re going to have to wait a long time until the lights go green.

5 comments

  1. Rick Mason says:

    Megan, as an engineer I challenge your assertation that there is no benefit in allowing a vehicle some warm-up time before driving. Even a minute of warming-up allows oil to fully circulate, especially to overhead cam gear etc. which is drained of oil when stopped. Engines work most efficiently with a coolant temperature of around 90°C and use a thermostat to assist in reaching this temperature quickly. Heavily loading a ‘cold’ engine (accelerating, climbing hills etc) uses excess fuel and not only increases engine deposits and exhaust emissions during this period but can also increase engine wear and oil contamination due to optimal clearances etc. not being attained.

    Modern oils and engine manufacturing tolerances together with electronic fuel injection and engine management all contribute to better performance across a wide range of operating conditions, but there is still benefit in allowing a short warm-up period before placing the engine under load. Hard or prolonged accelleration should always be avoided where possible until the engine has reached its normal operating temperature or very close to it – this is especially important when towing or carrying heavy loads.

    BTW, the ‘choke’ to which you refer went the way of the dinosaur when carburetors were replaced with fuel injection.

    February 25th, 2013 at 12:33 pm

  2. John Aquilina says:

    Hey Rick, you assume that longevity, and carcraft is something that interests typical disconnected car-owners these days. I take great pleasure in getting over 300,000kms in my small fleet (4-6yrs use as Limos) whilst passengers comment on how good they feel. A car that is revved hard and driven off from cold (like my two next door Y generation girls) will go like crap before 100,00km – giving them the totally justifiable reason to go out and buy another car to keep up with latest fashions.

    March 26th, 2013 at 9:21 pm

  3. chris welsh says:

    I have a new BT50 with fuel economy shown on the computor.
    Some diesel bought returns 7.5L per 100Ks approx.
    Others as basd as 10L mper 100Ks.
    I have experimented with an additive and found that the 7.5l fuels do not improve with additives however the poor performing fuels improve to aprox 8 L per 100Ks.
    I have done this over many tanks of fuel including 2nd half of tanks to monitor improvement.
    Offten the same fuel company will differ between petrol stations leading me to believe there are more than one fuel grades supplied by a single company.
    Independants are the same. Find a good one and stick to it.

    February 25th, 2013 at 2:46 pm

  4. Scott says:

    Choke? Any car in the last 30 years with a manual choke?
    All else being equal small cars WILL use less fuel than a large car. It is just physics that you need more energy to moor more mass.

    February 25th, 2013 at 7:03 pm

  5. Dennis Eden says:

    This is a very good publication, please send again

    February 26th, 2013 at 7:35 am