How Long Can a Car Idle? Finally Answered!

Let’s face it. We’ve all asked ourselves: How long can my car idle? Usually, this question pops into our head when we’re short on money, or when we’re waiting in traffic.

What is Idling and Why Is It Sometimes Necessary?

Idling is what happens when you let your car keep running without actually moving. If your car is not in motion, and the engine is active, the car idles.

There are several causes of idling, and they often cannot be avoided. For example, there is nothing you can do about your car idling while you are stuck in traffic. Also, you can’t really afford to shut off the engine at each traffic light or stop sign.

Furthermore, if you are driving a vehicle that runs on diesel, not letting it idle can be considered a borderline criminal offense. To elaborate, idling a diesel engine allows the exhaust fumes to clear. That saves you from getting a ticket for polluting the air.

Finally, if you are not an avid driver and your car sits unused for days on end, you might want to consider idling it once a week. Doing so for about a minute will keep the engine in good shape.

So… How Long Can I Let My Vehicle Idle?

Technically, the answer to this question is – indefinitely. We say technically because your car will eventually run out of gas. And it will not idle without gas.

empty gas gauge

However, if you let your car idle for as long as there is gas in the tank, you can be sure that your engine will keep running. That is to say; it will keep doing so unless something, such as a thermostat or a fan belt, breaks.

If all your systems are functioning properly, the engine will heat up to the operating temperature and resume working until you turn it off. Most cars nowadays contain water-cooling systems. Therefore, it is not necessary for the air to flow into the engine to cool it down. Your car will not inevitably overheat if left idling.

Am I Wasting Gas and Money If My Car is Idling?

The simplest way to answer this would be to say that you do not necessarily waste gas while idling the car. Unless you step on the gas pedal, your car uses between 14% and 20% of your entire supply of gas. That means that even if your car is idle for 24 hours, you will still have at least half the tank left.

On average cars will burn 1/7 – 1/5 of a gallon of gas an hour while idling. Most cars can hold 12 to 15 gallons of gas. Some vehicles have great fuel economy like the Honda Accord at nearly 50 MPG. While in contrast, the Land Rover for instance only gets around 20 MPG according to this source.

However, a very important question that we also need to address is how long should a car idle.

How Long Should a Car Idle?

User experience has shown that letting your car idle for 30 seconds to a minute would suffice. So, if you think the wait would take longer than that, consider shutting off your engine.

Leaving it running for longer than that would bring additional pollution to the air we all breathe. What’s more, in some cases, leaving the engine running while the car is not moving can be dangerous for the passengers. For example, if your car is idle and the air conditioner is on, you risk carbon monoxide poisoning.

Another important point to consider would be your car battery. If you have a faulty alternator, it will cause the battery to not charge, thus shortening the life of your battery.

When Should the Car Not Idle?

Surely you’ve been warned against leaving your car idle while filling up the tank. Although this may sound like a petty request, it is not unfounded. Due to high temperatures, the fumes that gas pumps emit can easily ignite. Therefore, even when you are using a gas container, shut your engine off.

Final Thoughts

In the end, leaving your car idle for 30 seconds to a minute can do it no harm. Technically, letting it run idle longer will not cause much harm, either. However, keep other aspects of doing so in mind. Letting the engine run for no reason is a hazard to the environment. Moreover, it poses a small, but important, risk to your health and well being.

So, the next time you wonder how long a car can idle, ask yourself – do you really need the engine running? Do yourself a favor. Shut off the engine.

Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.
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