You can sit with the car running for several hours, but it's generally not recommended due to fuel consumption, engine wear, and significant health risks from carbon monoxide (CO) poisoning. The primary limiting factor is safety, not the car's durability. In a well-ventilated, open area, a modern car with a full tank of gas could idle for over 24 hours. However, idling in an enclosed space, like a garage, can lead to fatal CO buildup in just minutes.
The biggest danger is carbon monoxide, an odorless and colorless gas produced by the engine. Never idle a car inside a garage, even with the door open. The risk of CO seeping into your home is extremely high. If you're using the car's heater or air conditioner to wait comfortably, always ensure you are in a completely open outdoor area.
From a mechanical standpoint, idling for long periods isn't ideal for your engine. Modern engines are designed to handle it better than older models, but idling causes incomplete fuel combustion, leading to carbon buildup on spark plugs and within the cylinders over time. This can reduce engine efficiency and performance. Furthermore, idling is a waste of fuel. An idling engine typically burns between 0.2 and 0.5 gallons of fuel per hour, which adds up quickly and is an unnecessary expense.
The following table outlines key considerations and data points for idling:
| Consideration | Data/Evidence | Source/Reasoning |
|---|
| Fuel Consumption (Average Car) | 0.2 - 0.5 gallons per hour | U.S. Department of Energy (DOE) estimates |
| CO Poisoning Risk (Enclosed Space) | Lethal levels can be reached in under 10 minutes | National Highway Traffic Safety Administration (NHTSA) |
| Typical Idle Duration (Safe, Open Area) | Up to 8-12 hours on a full tank | Based on average fuel tank capacity and consumption rates |
| Battery Drain (Accessories On) | Can drain a healthy battery in 2-4 hours with headlights and AC on | Automotive service industry data |
| Annual Fuel Waste (Collective U.S. Idling) | Over 6 billion gallons | Argonne National Laboratory study |
For short waits, turning off the engine is more economical and environmentally friendly. If you need to run the car for warmth or cooling, prioritize an open space and be mindful of your fuel level and battery health, especially if using electrical accessories.
