Updated 05 March 2013

Cool cars

Which wins for fuel efficiency: the delicious chill of car aircon, or windows down with the breeze in your hair? Find out with these cool car tips.

 In terms of maximising fuel efficiency, you’d ideally never use the car air conditioner nor drive with the windows open – but we know that simply isn’t realistic in a hot climate.

Still, if you want to save on petrol, keep in mind that car aircon reduces fuel efficiency by about 10%, so it’s always best to resist the temptation of that delicious chill as much as possible, and limit it to short blasts only.  

When you’re doing around-town driving at slower speeds, try to rely on rolling down the windows more for cooling. When you’re going faster on the highway though, at speeds above about 70-80 km/hr, having the windows open starts to significantly lower fuel efficiency because they increase wind resistance. At that point, for essential cooling aircon generally becomes a better bet.

The aircon-vs-open windows debate is also complicated by other variables, such as the size and shape of your vehicle. A big boxy SUV is already poorly designed as regards aerodynamics, so it’s probably not going to make much difference if you open the windows. However with sedan cars, the difference in wind drag at higher speeds will likely be significant.

Aim to combine use of aircon and open windows with your car fan and vents for cooling – these help to get a breeze moving without being a big fuel drain and air drag.

More car-cooling tips
To help reduce in-car temperatures and reliance on aircon, it also makes a big difference to park in the shade whenever possible, and use a windshield sunshade.

Just as you would to save on cooling (and heating) your home, add or remove clothing layers accordingly: adjust your body temperature before you adjust your indoor, or in-car, environment.

Plan trips so they don’t fall in the peak mid-day to mid-afternoon heat, and avoid rush-hour so you aren’t crawling along in a baking metal can.

More fuel-saving tips:
The walking bus
Be a road warrior
Merge short trips
Lighten your load
Idle cars are poor performers
Pump it up
Tame your inner roadhog

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