Driver Knowledge Tests

Should you turn your vehicle off when idling?

More and more vehicles are coming with automatic stop/start technology which stops your engine if you are stationary with your foot on the brake, and restarts it as soon as you lift your foot off the brake. If you have a slightly older vehicle should you turn it off at the ignition while you’re idling, or does it produce more wear-and-tear which offsets the savings in fuel?

In a standard rush-hour commute of an hour we can waste more than 10 minutes idling which can cost you around 100-400ml of fuel. Every week that means at least a litre of fuel wasted, or around $100 per year. Not only is there the financial impact, but also the environmental impact of all those extra unnecessary litres of fuel burned.

National Resources Canada estimates that if you save one minute of idling time then the cost savings outweigh the wear and tear.

You’ll find yourself idling in these situations:

  • Traffic lights
  • Warming up your car if it’s cold (you should only do this for 30 seconds, maximum, otherwise you’re simply wasting fuel)
  • Waiting at a drive-through
  • Waiting at a construction zone
  • Dropping off the kids at school
  • Stopped at a railway level crossing
  • Stopped at a construction area

If you are going to be idling for any more than 10-15 seconds, it’s more efficient to turn your vehicle off. With modern fuel injection and electronic ignition, the wear and tear on your engine components is minimal from a restart. Even though your engine will be stopped, there will be a residual coating of oil that remains on the components, even though the oil will start to drain into the sump.

Truck and bus drivers are able to use this to save money, bringing lower running costs. In America alone, around 14 million litres of fuel are burned every day through idling.

You should never turn your engine off while you are coasting otherwise you will lose your power steering and brakes. You shouldn’t use this manual stop/start method if you drive an older vehicle with carburettors. It’s also not such a good idea to use this method if you are at the head of the traffic queue otherwise you will delay everyone behind you getting through the traffic lights and that will cause more traffic jams and negate the environmental benefit.

In Germany, it is illegal to leave your vehicle idling while waiting at a train crossing, so there’s no point in you doing it either! Turn your vehicle off when it’s idling, but remember to be onto it when turning it back on so that you can get going again without holding anyone up.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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