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I know idling the car wastes gas but which is worse, idling for 5 min while I talk to my friend or turning the car off, talk for 5 min, and then restarting again? This can also be applied to idling while the car is being washed by those automatic car washers (takes like 3-4 min for the machine to do its thing), waiting in line at the drive thru McDonalds, drive thru Walgreens pharmacy, drive thru bank teller.

This hit me this past month because I did this several times with friends; chat for a short time (literally 5 minutes) with them while my car was running, and then instinctively turning it off to continue the conversation because I was told not to idle so as to not waste gas. Then my friends gave varying advice regarding this. I wouldn't call my friends car experts like you guys so I yield to your feedback.

Argument for idling:
1. Restarting a car often will wear the car out faster in the long run because the starter is being used a lot.
2. It takes more gas to start the car than it takes to idle.

Argument for shutting it off:
1. No gas wasted like idling does.
2. Engine is running without you going anywhere. Those rotations of the engine are counted in the computer on newer cars and thus will make you bring the car in earlier (mileage-wise) since you're not going anywhere while idling.

So, which advice/myth is correct? Thanks ahead of time to the community for your input.

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    Your engine is still fully warm after having been shut off for 5 minutes. (if it was warm already) So starting it again costs minimal effort for the starter and engine, and it'll right away continue running as efficient as when at operating temp. Shutting it off when pausing for more than half a minute is the best choice, except, maybe, when you do it 50 times a day. Shutting it off eliminates the noise, the fuel consumption, and pollution.
    – Bart
    Commented Apr 8, 2018 at 13:03

3 Answers 3

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As long as the vehicle is well maintained.. turning the engine off, or leaving it running would not really make any difference to engine wear and tear. Well unless this was being done 50 times a day etc. I'm considering delivery drivers here who will do just that, and more. In these cases battery, starter and ring gear issues can become more of an issue as these are the most heavily used components when repeatedly starting a vehicle.

Having the engine running for no reason though is a waste of energy & fuel so turning it off for 5 minutes each time in this sense is more beneficial.

You could also consider taxis in this discussion, they will mostly run their diesels every day and all day without turning off too often, and these vehicles will do 250,000 miles plus without issue. Again maintenance is key.

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    Agree with you mostly, though vehicles which are made to be taxis or liveries are constructed a little differently. Take for instance the Checker Cab ... the engines in them were completely different as far as cylinder liners and rings. Those engines would last forever. Diesels run lean normally, so efficiency is way up there. You can idle them while using very little fuel.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Apr 8, 2018 at 13:03
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    Pollution is a factor for idling vehicles. Trucking companies are finding alternatives to idling trucks, to reduce that pollution and also wear on the engines. When I see someone idling in a grocery store parking lot, I think, "The price of fuel is too low."
    – fred_dot_u
    Commented Apr 8, 2018 at 16:02
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This debate, usually just ends up as an argument all the time.

Idling is bad for the environment and for fuel consumption. Idling uses very little fuel, relative to other driving conditions, but it's using fuel at 0MPG, no matter how you cut it.

Couple this with the fact that you're burning fossil fuel for near-as-makes-no-difference no work. You're simply wasting the planets resources, while polluting.

It's going to get a lot more complicated if you want to pin-down what's "best" for the engine. I really don't want to get into this subjectivity. There are valid arguments for both sides on engine wear, the violence of the startup program, etc.

Just knowing that idling is bad for the environment is enough for me to do my best to limit idling for any foreseeable delay where I don't require a substantial amount of work from the engine.

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There are some conditions you would want to keep your car running in:

  • Motor is still cold.
  • You have a lot short trips, so Battery will not properly load.
  • You need power for large audio system, aircon, heater etc.
  • Car was just driven very hard and should cool down some minutes, especially turbo-cars.
  • You need to be able to move swiftly because you are blocking something.

On everything else, there is not much gain in idling. Starter motors can be replaced if they really ever ware out. Also idling does not produce too much wear so you won´t notice significantly reduced service intervals.

It really comes down to fuel-saving vs. any of the above conditions.

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