While idling won’t necessarily damage the battery, it can cause the battery to slowly discharge if the A/C is on and the blower is on high, and you have some large amplifier in the trunk drawing a lot of current. In these cases, the alternator won’t be able to keep up because it isn’t spinning fast enough to keep up with the loads during extended periods of idling.
Related to this, one of the most common questions drivers tend to ask is “how long can you leave a car running?”
The Principle of Idling
Idling is simply the practice of leaving your engine on while the vehicle isn’t moving. This practice is often unavoidable, especially when the vehicle is stuck in traffic, stopped at a red light, or when the driver is waiting inside the vehicle instead of parking.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: Since most vehicles and people use mileage to determine when the oil needs to be changed, the amount of time the vehicle spends idling won’t be recorded on most cars (some truck instrument displays will keep up with idle time).
Idling causes the engine’s revolutions per minute (RPMs) to drop to its resting point. During this activity, the engine is essentially running without any load except for some accessories.
According to a report from the US Department of Energy, Idling for more than 10 seconds consumes more fuel and produces more harmful exhaust emissions than stopping and restarting your engine.
How Long Can You Leave Your Car Running While Parked?
Idling can become an issue when it becomes a habit that lasts for more than 20 minutes. But according to the US Department of Energy, modern vehicles don’t really need to idle.
In fact, driving the vehicle can help the engine reach its ideal operating temperature much faster than idling. In addition, the catalytic converter can also operate much sooner if the vehicle is driven.
Most vehicle manufacturers recommend car owners to drive off gently 30 seconds after starting the engine, as it can help the vehicle warm up by being at work. This will also help the cabin temperature to increase faster during cold days.
There was a time when idling was recommended to warm up the engine, so you can’t really blame the drivers who keep doing it.
Old models with carburetors required idling due to the rich air-fuel mixture they start off with, especially during cold days. Idling to warm up the engine helps the carburetor to properly balance the air-fuel mixture.
Today, engines have become more sophisticated, especially with the introduction of electronic fuel injection technology.
Most modern vehicles don’t need to idle anymore since fuel injection technology can compensate for changes in the ambient air, resulting in optimized engine performance.
From Richard McCuistian, ASE Certified Master Automobile Technician:
One farmer in Texas reports that he left his pickup truck idling all night and didn’t realize it until the next morning when he went back to where he had parked the truck and discovered that the engine had overheated and destroyed itself. Granted, that’s an extreme circumstance, but think about what’s at stake and what that cost him.
When you engage in extended periods of idling, especially with the A/C running, you’re putting a lot of stress on your engine’s cooling system, not to mention the gas that is being burned in the process.
Consequences of Excessive Idling
Leaving your car running while parked can negatively impact the environment and result in drivability issues after some time.
Impact on Vehicle Condition and Performance
Sludge Build-Up
An engine that’s been idling for a long time also means that it’s been running at a low speed, resulting in an incomplete fuel combustion process on older vehicles. On newer engine platforms, this isn’t as much of an issue due to the PCM/ECM’s control of idle speed, and even temperature on engines with PCM-controlled electric thermostats.
Incomplete fuel combustion leaves residue on spark plugs and cylinders that can build up after some time and affect engine performance.
It’s also possible for the residue to get mixed with engine oil and reduce the lubricant’s capability to protect metal parts from wear and tear.
For diesel engines, long idle times can cause the exhaust temperature to drop below the ideal level for the diesel particulate filter to work properly. This can also lead to soot build-up and clog the filter.
Poor Fuel Economy
You’re losing about a gallon of gas for every hour your car is running at idle. And with the fuel prices at an all-time high these days, it’s a must to observe fuel-saving practices.
When a vehicle is idling for a long time, it usually means that the air-fuel mixture is rich, so the mixture is using up more fuel than air during the combustion process.
Premature Wear and Tear
All engine parts are bound to wear out after some time, but most of these components can last for years without needing a replacement if you stick with good driving habits and keep up with regular maintenance.
Idling is not considered a good practice. Excessive idling creates a condition where there’s more heat and less oil and coolant flow. As a result, parts such as cooling fans and water pumps are forced to work overtime.
Impact on the Environment
There are about 40 types of contaminants found in gasoline emissions during idling. In addition, approximately 130,000 tons of carbon dioxide are emitted from idling fleet vehicles.
Leaving your car running for a long time can result in cardiovascular and respiratory conditions, following the inhalation of these harmful emissions.
An idle vehicle can produce up to twice the exhaust emissions than a moving vehicle, increasing the amount of CO2 that gets trapped in the atmosphere. By leaving your vehicle running at idle, you’re essentially contributing to global warming.
Idling In EVs and Hybrids
Idling in hybrid and fully electric vehicles isn’t as detrimental as internal combustion engines.
Hybrid vehicles contribute to idle reduction since most of their engines automatically shut off when they’re not in motion. At the same time, these vehicles enable slow movements even when the engine is shut off.
As for fully electric vehicles, since they have no tailpipe emissions, idling is fine and safe.
Perhaps the only thing you should worry about EVs when idling is that they can reduce battery life. Unlike vehicles with internal combustion engines, EV batteries cannot recharge via an alternator.
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