How Long Can You Leave Your Car Running?

Dustin Hawley | Feb 03, 2021

We’ve all heard various myths about the “dangers” of starting and stopping our cars. Most people have probably heard that you wear down your vehicle’s engine every time you turn the ignition key, so it’s more ideal to leave your car running if you’re only planning on stopping for a few minutes at most.

idling cars in a traffic jam

But are these myths true? And if so, how long can you leave your car running without moving before potentially damaging your vehicle? Let’s investigate this subject in more detail.

What is “Idling”?

Leaving your car running after it has been started is known as “idling.” Idling essentially means that you leave your car’s engine running without moving the vehicle at all. In an “idle” state, your vehicle is still powered on and could theoretically begin moving at any time. In all actuality, it would start moving immediately were it not for other systems and components, like brakes and transmissions.

Most people have idled their cars at one point or another out of sheer necessity. For instance, idling often occurs automatically when:

  • You’re stuck in traffic, but you know you’ll be moving again in a few moments and don’t want to turn your car off and back on again unnecessarily.
  • You park your car and run into a store quickly without turning it off.
  • It’s perhaps a cold winter morning, and you decide to turn your car on before driving to work to warm up the interior cabin.

But although idling is a relatively common practice, is it truly worthwhile? 

What Happens Inside Your Car When It Idles?

Put simply, your car’s engine continues to run when it idles. Therefore, it still uses a minimal amount of fuel to maintain internal combustion. Because your engine continues running, many other automotive processes also continue by necessity. For instance:

  • The battery keeps draining.
  • The AC keeps flowing.
  • The engine keeps warming.

If you’ve ever heard the myth that idling your car damages it, don’t worry. It’s not true.

How Long Can Your Car Idle Before Trouble Ensues?

Although idling your engine is not necessarily harmful, it’s also not something you should try to do excessively. There are limits on how long you can leave your car running before you experience trouble or introduce the possibility of mechanical failures.

Remember, idling means your engine runs continuously at low power. In a vacuum (and with infinite fuel), your engine would continue to run forever. But in reality, several things might occur if your car idles for too long.

To avoid running your car for too long, you should only idle your vehicle for a few minutes at most before either moving your vehicle or turning the engine off.

Many people opt to let their car idle for longer than a few minutes when they anticipate needing to stop and start their engine multiple times. One good example is when driving on a backed-up road in a major city. But the idea that starting and stopping your engine multiple times is harmful is also a myth.

In fact, even if you’re stuck in traffic and know you’ll only move a few meters every few minutes, feel free to start and stop your engine multiple times. Modern engines from the 1990’s onward have been designed with fuel injection components, which deliver fuel to your engine efficiently and prevent oil dilution.

Unless you’re driving a car built in the ’80s (or older), you don’t have to worry much about wearing your engine down just from starting and stopping it multiple times.

What Happens if Your Car Idles for Too Long?

If you do leave your car running for too long, you might experience a few unpleasant side effects:

  • As mentioned, your car’s engine continues to consume fuel so long as it’s powered on. But it also consumes power from your car’s battery because the engine and alternator both run slowly whenever your car idles. The alternator provides enough power to charge the battery by itself. Still, if you’re idling and have other electronic components powered on – such as your radio or lights – you could gradually drain your car’s battery and potentially leave yourself stranded.
  • Your engine may also overheat if you leave your car idling for too long. However, this particular error often occurs because of mechanical malfunctions. If your engine overheats, get your cooling system or fan belt checked by a certified mechanic
  • Your car may run out of gas. An empty gas tank can sneak up on people who don’t expect their fuel gauge to go down when they’re simply sitting and not driving. But it can and has happened to people in the past on multiple occasions.

When Should You Leave Your Car Running?

Even considering the above risks, there may be a few instances where it’s appropriate to leave your car running rather than turning the engine off. Examples include:

  • When you’re warming up your vehicle during the winter and plan to run the engine for a minute or two.
  • When you’re sitting at a stoplight, even if the light’s pause period extends for a few minutes. In this case, turning your engine off and starting it again could take too long for the people waiting behind you.
  • When you’re low on gas and trying to get to a gas station. It takes more gas to start your engine than it does to keep it running in many cases. So keep your car on and idling if you’re running on fumes and trying to get to safety.

Summary

All in all, you can leave your car’s engine running for a considerable period of time before you start to run into problems. But it’s still a good idea to avoid making idling a habit. Leaving your car running doesn’t do anything positive for your vehicle’s long-term health, but it does have the potential to cause unexpected issues or mechanical failures.

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