Have you Ever Wondered How Long Can a Car Idle?

how long can a car idle

As you turn on your car’s engine and wait for your mom or sister to finish putting on make-up, you wonder if you’re wasting your gas while warming up your car.

You get caught in this dilemma whether you should just shut off the engine or let it run along with the air conditioner so you can save on gas. This process is called idling.

Idling is when the engine is running, but the car is not in motion. One example of idling is when your car is waiting at a traffic light.

how long can a car idle

Car Idling.


When Does the Car Need to be Idle?

There are a number of reasons why a car needs to be idle for a short period of time.

As mentioned above, you don’t have a choice when you’re stuck in traffic or waiting for the traffic light to change. Unless you really want to save on gas, you can just turn off the engine while on a traffic jam.

If your car runs on diesel, you need to let it idle for a few minutes to let the exhaust clear. Have you ever noticed those trucks that just started and dark smoke billows from the exhaust?

how long can a car idle

If your car runs on diesel, you need to let it idle for a few minutes to let the exhaust clear.

Unless you want to be fined for polluting the air, you should let the exhaust fumes clear from your diesel-powered vehicle by idling.

​Another reason why you need to let your engine ride idle for a few minutes is when you have not used it for a long time.

Engine vehicles get “stuck up” when unused. Every week, you have to turn on the engine and let the car run idle for about 30 seconds to a minute. This will ensure that the engine will still be on shape when you take it to the road. Sort of like an engine exercise.

Temperature also affects your car’s engine. During winter, it is best to let your car run idle for about a minute before traveling. This will help warm up the engine and thaw any frozen parts.

So, when your car makes this puttering sound, it could be that the engine got too cold.

What Happens When Your Car is Idle for a Long Time?

how long can a car idle

Although it is normally alright to let your car idle for a few minutes, leaving it idle for 30 minutes can be a big deal. Not only do you waste gas, but it also causes environmental damage because of the exhaust fumes.

Most modern cars do not need to be warmed up and left idle. Such is the case with automatic transmission cars. You can rev up the engine and drive away without idling it.

Do You “Waste” Gas When Your Car is Idle?

When your car is idle, you don’t necessarily use the gas. When you step on the gas pedal, that’s the time that it uses it. However, when you leave it idle your car uses approximately ⅕ to 1/7 of a gallon of gas per hour.

So, if you accidentally left your car idle on a full tank, you’ll still have half left after 24 hours. But of course, you don’t want to do that because your engine might overheat.

What About When Filling Up?

how long can a car idle

Gas stations warn car owners to turn off their engines and avoid letting the car run idle while pumping gas. This is to avoid accidentally igniting the gas fumes. Imagine scorching hot engine plus scorching hot weather.

The gas fumes emitted from gas pumps can flare up due to high temperature. Therefore, NEVER leave your car idle when pumping gas, or even when you’re using a gas container.

What Happens When the Air Conditioner is Turned On While Idle?

There have been news about carbon monoxide poisoning in cars. When your car is idle and the air conditioner is turned on, carbon monoxide fumes may seep in through the air vents. 

how long can a car idle

Your car may also overheat if you let the engine run idle with the air conditioner turned on. Cars were made for a purpose, and that is for traveling. Leaving your car idle and sleeping in it is not a good idea.

Another factor is your car’s battery. The AC will keep on consuming your car’s battery power. Therefore, leaving your car idle will lessen your battery life.

Also, when the car’s engine is not working, so is the alternator. The alternator charges your car’s battery. Your car’s battery will eventually drain out if you leave it idle for hours. More so if the air conditioner is turned on.


Now that you have learned about the various reasons why cars should idle and the effects, you may still be wondering, “How do I know when it’s time to turn off the engine?”

Based on this YouTube video, your car needs to remain idle for only 30 seconds.

If it will take longer than that, just turn it off. Another way to determine when it’s time to turn it off is to look at the temperature gauge.

Looking at the photo below, when the needle rises to the middle, it means that your car’s engine has already warmed up. It usually warms up in a minute when the weather is cold. That’s the purpose of this gauge, to monitor your car’s coolant.

how long can a car idle

You may be thinking, “So what if I’m stuck in traffic? Do I need to turn off my engine?” You don’t need to, but it would be a good idea to do so. Here’s another video of what happens when you leave your car idle.

Look at those exhaust fumes! Imagine a hundred cars stuck in a traffic jam. Imagine the effect on the environment. While you don’t consume too much gas when your car is idle, you still waste some of it.

The next time you leave your car parked while waiting for your friend or family, it would be best just to turn it off and avoid those toxic fumes.

Stuck in traffic? It’s understandable that the heat can get unbearable and you cannot manage without air conditioning. But, if it can be helped, why not turn off your engine?

Who knows, people may take the hint and follow your example. You’re not just saving on gas but you’re saving the environment, too. What do you think?

About the Author

I am David Walker ,I'm a car enthusiast. Through this blog, I want to share every single experience I had with my beloved car with you guys. Definitely feel free to comment, give feedbacks and show us what You and your cars have been through.

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(1) comment

  • MIke November 12, 2017

    The AC uses the cars battery? Yeah that’s false. The AC Compressor is mechanical not electrical it just increases fuel consumption because when the AC is on the clutch on the AC Compressor is engaged and it adds a extra strain on the engine (it’s driven by the serpentine belt)

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