Should my Engine Idle?

Idle or Switch Off my Car Engine?

 

When I first learnt to drive, I was told that it used more fuel to stop and re-start a car, than it did to leave it running, or idling.  As I write this, I’m thinking that I obviously learnt to drive a long time ago!

It may have been true in the ‘dim and distant past’ but it certainly isn’t true nowadays with our modern cars.  Starting a car’s engine uses only a negligible amount of fuel and doesn’t have a massive impact on the wear and tear of the engine.

Idling your car simply uses fuel and costs you money, while also spewing pollutants into the air.

I decided to find out what the cut-off point is now – in other words, at what point does it make sense to idle rather than switch off the car.

I was surprised by what I found out.

In a modern car, it’s 10 seconds.

10 seconds?

Is that all?

OK, 10 seconds isn’t always practical – for example in traffic.  So the rule of thumb is that if you’re going to stop somewhere for more than 10 seconds (except in traffic), it makes sense to switch off the engine.   Use common sense to work out if it makes sense to switch off or to idle at these common idling spots:

  • drive-through service lines,
  • rail crossings,
  • car wash queues,
  • carpool lines,
  • departure from concerts and sporting events,
  • while talking to friends
  • while using the cell phone.

By understanding the effects of idling and reducing the practice, you can improve your car’s performance, save money, and reduce pollution.

Is Idling Bad for Your Car?

Interestingly, excessive idling can actually damage your engine components.  An idling engine is not operating at its peak temperature, which means that fuel does not undergo complete combustion. This leaves fuel residue that damages engine parts and can contaminate oil.

An idling car is the most inefficient car on the road — it gets zero miles per gallon

Warming Up a Car

Idle Engines use Fuel

What about warming up a car, especially in winter (unless you live in a hot climate)?  Doesn’t the car need time to warm up before you can safely drive it?

Cars should be warmed up – but idling is not the way to do it, not even in cold weather!

The best way to warm up your car is to drive it.  You need no more than 30 seconds of idling before driving away, even on the coldest days.  Just avoid high speeds and rapid acceleration for the first 3 miles / 5km.

The catalytic converter – the device that reduces pollutants from the vehicle exhaust – doesn’t function properly when it’s cold, and the best way to warm it is to drive the car.  You emit more pollution if the catalytic converter is cold.

The tyres, transmission, wheel bearings and other moving parts also need to be warm for the vehicle to perform well. Most of these parts do not warm up until the vehicle is driven.

Next:  What about idling in diesel and hybrid cars?  Also, which technology is available in Europe and Asia, but not in the US!

In the meantime though, here’s a thought:

An idling car is the most inefficient car on the road — it gets zero miles per gallon.

 

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Photo Credit: microsoft.com

17 comments… add one

Your thoughts and opinions are important to me! Do tell me in the comments below!

  • Suzanne Laramore 13th April 2012, 9:20 PM

    I am going to enjoy pointing out to my smug brother about Not letting my truck warm for 2 or 3 minutes before driving.

    Thanks!

    Suzanne

    Reply
    • Clare Delaney 14th April 2012, 7:15 AM

      LOL, glad to be of assistance! 🙂

      Reply
  • Michael Paulse 19th October 2011, 3:47 AM

    Thanks for answering the question about how long till idling becomes inefficienrt. I thought it closer to 3 minutes.

    Reply
  • Eva Palmer 15th October 2011, 10:52 PM

    Hi Clare!
    You can’t imagine how many times I have wondered this!! If I know I am going to be long I always prefer to switch off the engine…it makes me nervous knowing that I am just using fuel and contaminating!

    Reply
  • Sonya Lenzo 15th October 2011, 7:21 AM

    You continue to amaze me with the wide variety of “eco” ideas you have for living more responsibly!
    Sonya Lenzo

    Reply
  • Michael D Walker 15th October 2011, 7:06 AM

    Great info that updates the things I’d been taught years ago. The one thing I wondered about is how far back does the 10 second rule work out? In other words, is this true if you have a car from the 80’s? 90’s?

    Michael

    Reply
    • Clare Delaney 15th October 2011, 7:17 AM

      It’s difficult to find a definitive answer on this one (I had also wondered myself!). Lots of opinions, very little in the way of cross-referenced and verifyable facts. I would suggest any car manufactured in the last 5 years. Older than that, the “old” logic of longer times applies. Thanks for your comment Michael!

      Reply
  • Andrew Miner 15th October 2011, 2:59 AM

    In trucker terms, “I guess I’ll just shut her down then…”
    Thanks for the excellent article.

    Andrew

    Reply
  • Cherie Miranda 15th October 2011, 1:00 AM

    I’ve wondered about this. Thanks for clearing it up!

    Cherie Miranda

    Reply
  • Kevin Bettencourt 14th October 2011, 11:44 PM

    10 seconds does not justify very much idling. Especially if the catalytic converter which cleans exhaust isn’t functioning correctly. I curious how the Prius will come out. I’m thinking since it switches to the motor mode when I parked, but that’s a guess.

    Reply
  • Neil Dhawan 14th October 2011, 8:55 PM

    Clare,

    You continue to bring awareness to things that, again, are very rarely thought of, if at all … Thanks to your article, I have been enlightened from an old way of thinking. I always thought you should idle th car to get all the moving engine parts “warmed up” … thanks to you, I will be able to pollute the air less and get to where I am going quicker 🙂

    Stay Amazing and Do Great Things, Neil

    Reply
  • Dennis Perry 14th October 2011, 3:29 PM

    Great advise. I, too, have always heard that idling is better than turning off the engine. Thanks for setting the record straight.

    Dennis

    Reply
  • Rob Malone 14th October 2011, 2:15 PM

    Hi Clare,

    I also was taught that starting your car took more fuel than idling. Thanks for giving more current and accurate information.

    Reply
  • John Moulder 14th October 2011, 10:54 AM

    Thanks for the info Clare . I have often wondered if it was still applicable in todays vehicles to keep idling or switch off . In the past the problem lay in the battery and starter motor , with the amount of strain on those components when starting up .

    Reply
  • Annie Born 14th October 2011, 9:04 AM

    Another excellent article!
    Awesome Info!
    Looking forward to tomorrow!
    Create a great day!

    Reply
  • […] If you are driving a car, bus or truck, don’t idle your engine […]

  • Suzanne Laramore says:

    I am going to enjoy pointing out to my smug brother about Not letting my truck warm for 2 or 3 minutes before driving.

    Thanks!

    Suzanne

  • Michael Paulse says:

    Thanks for answering the question about how long till idling becomes inefficienrt. I thought it closer to 3 minutes.

  • Eva Palmer says:

    Hi Clare!
    You can’t imagine how many times I have wondered this!! If I know I am going to be long I always prefer to switch off the engine…it makes me nervous knowing that I am just using fuel and contaminating!

  • Sonya Lenzo says:

    You continue to amaze me with the wide variety of “eco” ideas you have for living more responsibly!
    Sonya Lenzo

  • Michael D Walker says:

    Great info that updates the things I’d been taught years ago. The one thing I wondered about is how far back does the 10 second rule work out? In other words, is this true if you have a car from the 80’s? 90’s?

    Michael

    • Clare Delaney says:

      It’s difficult to find a definitive answer on this one (I had also wondered myself!). Lots of opinions, very little in the way of cross-referenced and verifyable facts. I would suggest any car manufactured in the last 5 years. Older than that, the “old” logic of longer times applies. Thanks for your comment Michael!

  • Andrew Miner says:

    In trucker terms, “I guess I’ll just shut her down then…”
    Thanks for the excellent article.

    Andrew

  • Cherie Miranda says:

    I’ve wondered about this. Thanks for clearing it up!

    Cherie Miranda

  • Kevin Bettencourt says:

    10 seconds does not justify very much idling. Especially if the catalytic converter which cleans exhaust isn’t functioning correctly. I curious how the Prius will come out. I’m thinking since it switches to the motor mode when I parked, but that’s a guess.

  • Neil Dhawan says:

    Clare,

    You continue to bring awareness to things that, again, are very rarely thought of, if at all … Thanks to your article, I have been enlightened from an old way of thinking. I always thought you should idle th car to get all the moving engine parts “warmed up” … thanks to you, I will be able to pollute the air less and get to where I am going quicker 🙂

    Stay Amazing and Do Great Things, Neil

  • Dennis Perry says:

    Great advise. I, too, have always heard that idling is better than turning off the engine. Thanks for setting the record straight.

    Dennis

  • Rob Malone says:

    Hi Clare,

    I also was taught that starting your car took more fuel than idling. Thanks for giving more current and accurate information.

  • John Moulder says:

    Thanks for the info Clare . I have often wondered if it was still applicable in todays vehicles to keep idling or switch off . In the past the problem lay in the battery and starter motor , with the amount of strain on those components when starting up .

  • Annie Born says:

    Another excellent article!
    Awesome Info!
    Looking forward to tomorrow!
    Create a great day!