how long can you leave car running in park

[MadisonFitz]

You can safely leave a car running in park for as long as it has fuel, but it's generally not recommended to idle for more than 30 minutes to an hour at a time. Prolonged idling can lead to unnecessary fuel consumption, engine wear, and potential overheating if the cooling system is not operating at peak efficiency. The primary risks are not immediate mechanical failure but the long-term accumulation of carbon deposits and the environmental impact.

Key Considerations for Prolonged Idling:

Factor	Consideration & Data
Fuel Consumption	An average car idles at 0.2 - 0.5 gallons per hour. Over 5 hours, that's 1-2.5 gallons wasted.
Engine Wear	Idling causes incomplete fuel combustion, leading to carbon buildup on spark plugs and within the cylinders over time.
Battery Charging	Idling does recharge the battery, but very slowly. A 30-minute drive is far more effective than hours of idling.
Emissions	The EPA notes that idling vehicles contribute significantly to air pollution, releasing CO2 and other pollutants.
Legal Restrictions	Many states and municipalities have anti-idling laws with fines, often limiting idling to 3-5 minutes.
Oil Dilution	In some modern direct-injection engines, prolonged idling can allow fuel to dilute the engine oil, reducing its lubricating properties.

Modern engines are designed to handle idling, but it's an inefficient practice. If you need to keep the car on for climate control or to power electronics, it's mechanically safer to do so than frequently turning the engine on and off in a short span. However, for extended periods, the potential for overheating—especially in older vehicles or in hot weather—is a real concern. Always ensure the vehicle is in a well-ventilated area to prevent dangerous exhaust fumes like carbon monoxide from entering the cabin.

[MacSkylar]

Honestly, I just go by the 10-minute rule unless it's freezing out. If I'm waiting to pick someone up, I'll let it run for a bit to keep the heat or AC on, but I shut it off if it's going to be longer. I had an older truck that started overheating once after idling for almost an hour in a drive-thru line on a hot day. That was enough of a lesson for me. It just feels like a waste of gas to let it run for no reason.

[VanLayla]

From an environmental and legal standpoint, it's best to minimize idling. Many cities have ordinances against idling for more than three to five minutes due to emissions. Unnecessary idling contributes to air pollution and greenhouse gases. If you're parked and waiting, turning off the engine is the responsible choice. The idea that restarting your car uses more fuel than idling is a myth for modern vehicles; restarting uses about 10 seconds worth of idling fuel.

[AustinLynn]

I worry about the mechanical side. Letting an engine run for hours without a load isn't ideal. It doesn't get hot enough to burn off condensation, which can lead to sludge in the oil over time. You're also putting wear on components like the alternator and water pump without the benefit of actually driving the car. It's low-stress wear, but it's still wear. I'd only do it if absolutely necessary, like in extreme weather to survive.