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Is It Bad to Idle a Car Overnight?

The sun has set, you have plenty of miles ahead of you, but you can’t kick the urge to fall asleep. Often, the safest option is to pull over and sleep until you’re alert and awake enough to get back on the road. This leaves a lot of people wondering, is it bad to idle a car overnight?

It’s bad to idle your car overnight, but probably not as bad as you think. It won’t destroy your car in a single day, but it will do lasting damage, especially if you idle overnight repeatedly. I don’t suggest doing it, but it’s not the end of the world or your car if you do.

In this article, I’ll answer this question. I’ll tell you everything you need to know, answer your questions, and explain what went into my final decision.

What is Idling?

Idling is when you turn the key in your car, start the engine, then just leave it in “Park” and sit there. The tachometer will show a low rpm level and there shouldn’t be a ton of noise — unless you have a souped-up car with a custom muffler.

There’s no load on the engine since nothing is engaged. The engine is not being stressed as much as it would while driving.

How Idling Works

Let’s pop the hood and let me talk about how idling works for a second. When your car is idling, the engine is just purring. Pistons are compressing a mixture of fuel and air. This compressed mixture ignites, making a little explosion that powers your car.

How an internal combustion engine works.

This is how internal combustion engines work, at least.

The problem is that the mixture isn’t perfect when you first start up your car. The engine has to really heat up to operating temperatures before it’s a good ratio. The extra fuel in the mixture can coat the walls of the cylinders in your engine.

This coating can quickly deteriorate the walls over an extended period.

Additional fuel can also creep throughout the rest of your car, coating your exhaust system and gunking up your spark plugs.

Situations Where Idling Makes Sense

Even though idling might be bad, there are plenty of reasons why you might want to idle. Let me tell you a few of the big reasons.

Police Officers

If you’re a police officer doing traffic duty, it’s hard to avoid idling your car. Most officers will idle on the side of the road so they can quickly pursue speeders, respond to calls, and use the electronics in their cruiser.

The time it takes to start a car and let the oil circulate is more than a police officer can afford in high-stakes situations on a daily basis.

Highway patrol car idling on the side of the road

This is also the reason why you’ll find a lot of engine troubles on retired police cruisers for sale. If you’re buying an old Crown Vic, make sure you look engine and its components.

In addition, you can look at a police car if you want a quick answer. Their vehicles will idle for hours on end repeatedly and they work just fine.

Briefly Warming Up Your Car

Everyone in the northern half of America knows that idling is a life-saver in the early morning. There’s nothing like those cold mornings with ice all over your windows and freezing temperatures in your car.

In this case, it’s perfectly okay to idle for a few minutes and get things heated up. Keep in mind, I said only a few minutes. Once you start going longer than 5 minutes, the negatives will outweigh the positives when it comes to idling.

Getting Fluid Flowing

Car experts suggest that you should idle your car for about 10 to 30 seconds every time before using it. This process helps the fluids start flowing and circulating around your car. It allows oil to be in the right place when you need it most, and your engine can start getting lubricated before it sees a load.

In this case, idling is sort of like stretching before working out.

Inside of a car engine

What’s So Bad About Idling?

If you’re on the fence, I’ll talk about what makes idling so bad. These reasons are usually why so many people make idling a four-letter word.

Wastes Gas

If you’re looking to save money on gas, the last thing you should do is idle. The simple fact is that when your car is running, gas is being used. If you’re not going anywhere, I would call that a waste of gas.

There’s a rule of thumb that says every 2 minutes of idling has an equivalent impact of driving the car one mile. If your car gets 20 mpg, you’re wasting 15 cents every 2 minutes, or 7.5 cents a minute.

The same equation tells us that idling for 8 hours overnight wastes $36 in gas. Doing that multiple times a year is a waste of hundreds of dollars.

Gives a Sketchy Impression

When you see a car idling near your home, what’s your first impression? For me, my mind always jumps to someone doing a stakeout or keeping the engine running for something about to go down.

If you idle on the side of a road in a residential area, you might be giving off the wrong impression. People might call the police on you to see what’s going on.

You might have the right intentions, but it doesn’t matter to a concerned resident.

Hurts the Environment

If you didn’t know, the exhaust from your car contributes to global warming. It’s one of the reasons why the EPA is getting so strict about emissions and making bans.

One of the harmful emissions is carbon monoxide. This is a big greenhouse gas and is toxic to the human body.

Some Local Laws Prohibit it

Another reason not to idle? You might summon the police and get yourself a nice ticket.

In 9 states, it’s illegal to idle for more than 5 minutes. Some of these states have even more strict idling laws when it’s in close proximity to a school or government building.

Will you get a ticket for idling in your driveway? Maybe not. It all comes down to how unlucky you are, but the bottom line is that it’s illegal. It’s more common to get ticketed if you’re doing it on the side of a road or in the middle of the night.

Not Enough Oil for Lubrication

Another thing that I didn’t mention is the oil pump in your car. This distributes oil to the components that need it. If you didn’t know, oil is there as a lubricant that keeps everything moving nicely.

When there’s not enough oil, moving parts wear out a lot quicker. This is one of the big reasons why many experts always suggest routinely changing your oil.

It Hurts Your Engine

I mentioned it already, but it bears repeating: idling your car hurts your engine. Sure, there’s nothing wrong with idling for a few seconds or minutes, but anything more than that is dangerous.

The bottom line is that parts of your engine will start to deteriorate, break down, and stop working.

It Can Be Deadly

Idling your car can be deadly if the vehicle does not have proper ventilation like a garage. As I mentioned earlier, carbon monoxide is pouring out of the exhaust whenever your car is idling. The reason why your exhaust is way back there is to minimize your exposure to carbon monoxide as long as your car is on.

Carbon monoxide can make you sick, give you a headache, make you feel confused, make you pass out, or even kill you with enough exposure.

If your exhaust pipe is blocked at all, then the gas will back-travel into your car and smoke you out. In addition, if there isn’t enough room for the gas to escape near your exhaust, it can plume up and come in through your windows.

Is It Bad to Idle a Car Overnight?

After reading the info I just provided, it might seem pretty clear. Idling is generally a bad idea. Still, there are plenty of reasons why you should do it. If you can overlook the negative components, then you can keep idling.

With that said, there are a few things to consider when idling your car.

Things to Consider When Idling Your Car Overnight

If you’re dead-set on idling for extended periods of time, here’s a quick checklist for you. Missing one of these key points might leave you with a bigger problem than just pollution or a little engine damage.

Keep Your Gas Tank Full

Once your car runs out of gas, it will just stop running. This is an obvious point when you’re driving on the highway and monitoring your fuel gauge, but it’s easy to overlook it if you’re prepping for a nighttime car nap.

As I mentioned, idling can burn fuel faster than you think. If you don’t have enough gas in the tank, the car will die and you’ll be exposed to the outside temperatures until you wake up. Even worse, you won’t have any gas when you awaken, so you’ll be stranded.

Make Sure You’re Warm

If you live in an area where it gets cold, it’s imperative that you bring some blankets and jackets to keep you warm.

In case it gets cold at night, make sure to bring a blanket or two.

It’s not uncommon to hear about people freezing to death in their cars. This is a routine headline in cold places like Michigan and Alaska. When in doubt, pack another blanket and bundle up.

Engage the Parking Brake

A few other things that you can’t do when you’re asleep are steering the car or apply the brakes. If your car’s brakes fail, you’ll be sent rolling into the nearest obstacle.

I always suggest engaging your parking brake whenever you want to idle overnight. It’s a backup that can help avoid a disaster. Plus, it’s really easy to engage it.

Can You Sleep in an Idling Car Overnight?

Even though it’s safe to idle a car overnight, I wouldn’t exactly suggest sleeping in it. There’s a certain risk of breathing in harmful car emissions, running out of gas, and possibly even killing the battery.

Engine idling

It’s the same reason why they say you shouldn’t idle your car in a garage ever. The fumes that come out of your exhaust are called carbon monoxide, and they are lethal and will kill a human with enough exposure.

If you do decide to sleep in your vehicle overnight, make sure the vehicle is in a safe public environment, the exhaust is not backed up against a bush or something else that can restrict airflow, and that you have sufficient fuel in the tank.

Conclusion

I just covered whether or not it’s bad to idle a car overnight. The verdict? I don’t recommend it, but it won’t destroy your car immediately. Make sure you idle overnight safely and make the right decisions ahead of time. If you want more car tips, check out the rest of my blog. I also have some products that I highly recommend for any car owner.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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