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Saving Gas: Idling vs. Restarting

30 June 2008

Recently, I’ve been trying a new trick to improve the gas efficiency of my ’99 Honda Civic. I already drive the speed limit and try to avoid quick starts or stops, but I’ve been inspired by rising gas prices to get a little more creative. When I heard about turning my car off instead of letting it idle through red lights, I thought I’d do a little research into the actual usefulness of this action. After all, doesn’t it take more energy to restart your car rather than just let your car idle?

Well, it turns out, if you’re going to be idling for 10 seconds or longer, you save gas by turning off your car and then restarting it. This is one way that hybrids work to improve their gas efficiency. For those of us running non-hybrids, this can be a little more work – for example, I have to shift my car into park, turn it off, then turn it on and shift into drive as the light changes. It requires me to pay a little more attention to what’s going on, which I don’t mind because my gas efficiency has definitely improved!

6 Comments leave one →
  1. gustavB permalink
    1 July 2008 7:46 am

    Could you put your sources of your research in this article?
    Thanks!

  2. gustavB permalink
    3 July 2008 12:25 pm

    Cool! thanks!!! I guess I will start ot turn off my car when sitting at all those stupid stoplights.

  3. John Kraynak permalink
    15 October 2008 8:18 am

    I could be wrong but I think at stop lights you would be better off just shifting your car into neutral and letting it idle. I believe this would help keep your transmission cooler since there would be no load on it with the car in neutral. Starting and stopping your engine at red lights is going to wear out your starter sooner as well as you battery. If you don’t do your own work on your car your going to have to pay to have your starter replaced and labor is around $80.00 an hour plus parts. I don’t think the majority of us use $150.00 a year in gas ideling at stop lights. I used $150. as a minimum figure for what it would cost to pay to have your starter replaced.

  4. 15 October 2008 8:23 am

    John, you make a good point. According to my sources, however, “Frequent restarting has little impact on engine components like the battery and the starter motor. Component wear caused by restarting the engine is estimated to add $10 per year to the cost of driving, money that will likely be recovered several times over in fuel savings from reduced idling. The bottom line is that more than ten seconds of idling uses more fuel than restarting the engine.” (http://www.consumerenergycenter.org/myths/idling.html). It doesn’t appear that stopping and starting the car at red lights causes significant stress on the starter, enough to need to replace it yearly. I am going to take my car into the mechanic this week for a 100,000 mile check up (gotta love those Hondas) and I’ll ask while I’m in there. Thank you for your question!

  5. Leopold Stoch permalink
    3 December 2009 5:39 pm

    I’ve had this argument with a few people over the years. My rule of thumb is that if I’m approaching a red light which I know to be on a long cycle (like at a 6 point intersection or a 4 point with advanced left turns) I shut it down. I KNOW I’m saving fuel. I actually would’ve thought the break even time to be less than ten seconds, but whatever, I typically shut it down for instances where I know I’ll be stopped for whole minutes because heat is a killer of electric starter motors and over-use WILL overheat it.

    I have one added concern these days: turbochargers get very hot, and in order to maintain the temper of the metal in the turbo’s components, it needs a constant flow of oil for a short while after being under load.

    I still shut down at long red lights, and haven’t screwed up a turbo yet, but it is in the back of my head and I always idle for at least 30 seconds after high rpm driving.

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