We’ve all been told not to let our cars idle for too long. But what happens if you leave your car running for 5 hours? If your engine is in good shape, it might be okay. However, if your car has pre-existing problems, you could face issues like overheating, reduced lubrication, or even stalling due to excessive air conditioning use.
What Happens If Your Car Idles for 5 Hours?
Being stuck in heavy traffic can be frustrating. In stop-and-go situations, cars creep forward slowly, so drivers often keep the engine running and their foot on the brake instead of turning the car off and on repeatedly.
When a car’s engine is on but the vehicle isn’t moving, it’s called idling. Some people let their car idle to warm it up on chilly mornings, while others leave it running during quick errands to avoid restarting the engine.
Most of us only let our cars idle for a few minutes. But what would happen if you left your car idling for 5 hours? How would this affect the engine, fuel tank, or combustion system?
If your car’s engine is in good condition, idling for 5 hours won’t cause major damage. The main concern is fuel usage. An idling engine still burns gas to keep running.
Don’t be shocked if, after 5 hours of idling, you need to head to the gas station to refuel!
Does Idling Affect the Battery?
If your car’s battery is in good shape, idling for 5 hours won’t harm it. Many people think the battery would drain first, but that’s not true. When the engine is running, it powers the car’s electrical systems by burning gas, not draining the battery.
However, if you only turn the ignition halfway (to the “on” position without starting the engine), the car’s electrical systems rely solely on the battery. In that case, the battery could drain over time.
How Much Gas Does Idling Use?
An idling engine burns fuel, but the amount depends on your car’s make and model. On average, a car might use between 1/7th and 1/2 a gallon of gas per half-hour of idling, depending on its fuel efficiency.
What Risks Come with Idling a Car with Engine Issues?
If your car’s engine already has problems, idling for a long time can be risky. An engine with issues may overheat because the heat can’t escape properly. If you’re present, you can turn off the engine to prevent damage. But if the car is left idling unattended, the engine keeps running, trapping heat under the hood and potentially causing more harm.
Leaving the air conditioning on while idling can also strain a faulty engine, as the AC draws power directly from it. This could lead to stalling or overloading the engine.
When Should You Turn Off Your Car Instead of Idling?
Letting your car idle for several hours isn’t a huge problem if it’s in good condition. However, if your engine has existing issues, prolonged idling could worsen them.
Avoid making a habit of idling for long periods. If you know you’ll be away from your car for 30 minutes or more, it’s best to turn off the engine.
Is Carbon Monoxide a Concern?
Never let your car idle in an enclosed space like a garage. An idling car produces carbon monoxide, a dangerous gas that can build up quickly in confined areas.
In a closed garage, carbon monoxide can reach harmful levels in less than 5 minutes. Always open the garage door before starting your car to allow ventilation and prevent gas buildup.
Installing a carbon monoxide detector in your garage is a smart way to stay safe. It can alert you to dangerous levels before it’s too late.
Always prioritize safety when leaving your car running!
If your car requires keys in the ignition to run, don’t leave it idling for too long. Someone could easily steal it if they see the keys.
Newer car models often use key fobs instead of traditional keys. These cars may not start or move if the fob is too far away, offering some protection against theft.
Final Thoughts
Leaving your car idling for 5 hours once is unlikely to cause major issues if your vehicle is in good condition, though you’ll likely need to refuel. However, if your car has engine problems, prolonged idling could lead to overheating or stalling, especially with the AC on. For short stops, idling for 10–30 minutes is generally safe.