Silly Question #23: Windows down, or air conditioning?

Tuesday, 12 December 2017

This New Zealand summer is obviously turning into a scorcher, so this raises a modern-day motoring question: In hot weather, is it better to drive with the windows down, or the air conditioning on?

That's a bit like trying to answer that famous winter-time question: If you cross a street on a wet day, will you get wetter if you run the distance or walk it? Some say that either way, you'll encounter the same number of raindrops.

But back to the motoring question: fresh air or cooled air?

Around town it is said to be better to have your window open - and your elbow resting on the door.

With summer driving, there's nothing like having the windows down so fresh air can waft around the vehicle's interior. And if you are in either of the front seats, open windows also provide the opportunity to rest your elbows on the doors - which for some reason is always a sort of sociable thing to do.

* Silly car question #20: Why do we drive on the left

* Silly Question #13: How do I back a trailer?**

Out on the open road, it's more comfortable to have windows shut and the aircon on - even though it might cost more fuel.

But then again, when the weather is really hot and sticky, it's a very comfortable experience to have all the windows up and the car's air conditioning on. That way, while everyone on the outside is sweltering and sweaty, you can tool around all cool and comfortable. It might not be as sociable as having the windows down and your elbows out - but it's a lot cooler.

And then there's the small matter of fuel consumption.

Of course you could have the windows closed and the aircon off - and swelter.

Experts say that turning on a car's air conditioning adds about 5 per cent to a vehicle's average fuel consumption. But experts also say that driving around with the windows down, particularly at highway speeds, causes air turbulence and drag that also adds to average fuel use.

There have even been studies done on it. A few years ago in America, General Motors and the Society of Automotive Engineers tested a sedan and an SUV at various speeds to find out which used the most fuel. It showed that running the aircon requires more fuel than driving with the windows open.

The MythBusters TV series found the same thing. The team drove two SUVs with the same amount of fuel, one with the aircon on and the other with the windows down, around a raceway at 70kmh. The air-conditioned SUV ran out of petrol first.

Of course you could save fuel by driving around with the windows closed and the air conditioning turned off - but hey, who wants to do that? You'd probably end up spending more money than you've saved by being forced to call into the nearest dairy to buy some cold bottles of water.

Many say that if you really want to conserve fuel, the best thing to do is to open the windows while driving in urban areas, and to close the windows and use the air conditioning on the open road. But even then, the resultant fuel efficiency all depends on the type of vehicle being driven - a lump of an SUV or ute, or a more streamlined sedan or hatch.

And here are some other suggestions for improving fuel economy (and driving comfort) in hot summer weather:

* Park in the shade, or use a windscreen sunshade, to prevent the cabin from getting too hot when the vehicle is not in use.

* Don't idle with the air conditioning running before driving. Most systems are more efficient when the vehicle is on the move.

* Drive for a short time with the windows open before turning the air conditioning on, to let hot air out of the cabin first.

* Don't set the air conditioning temperature lower than is needed.

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