Leaving your car idling for extended periods is generally not recommended. While modern engines are robust, prolonged idling (over 10-15 minutes) can lead to unnecessary engine wear, wasted fuel, increased pollution, and potential legal issues in some municipalities. The engine runs rich, leading to incomplete combustion that can foul spark plugs and contaminate engine oil more quickly. For most daily situations, turning the engine off is the better choice for your vehicle's health and your wallet.
The primary issue is that the engine doesn't reach its optimal operating temperature while idling. This "cold" operation causes fuel to condense on the cylinder walls, diluting the oil and increasing wear on critical components like piston rings and cylinder liners. Furthermore, the alternator charges at a lower rate at idle, which can slowly drain the battery if power-consuming accessories like the air conditioner or headlights are running.
The environmental and financial costs are significant. Idling for just 30 minutes a day can waste over $650 in fuel annually, assuming a national average gas price. Many states and cities have anti-idling laws, especially near schools, with fines that can be substantial.
| Idling Duration (Minutes) | Estimated Fuel Consumed (Gallons, V6 Engine) | Approximate Cost (at $3.50/gallon) | CO2 Emissions (Pounds) |
|---|
| 10 | 0.05 - 0.07 | $0.18 - $0.25 | 1.0 - 1.4 |
| 30 | 0.15 - 0.21 | $0.53 - $0.74 | 3.0 - 4.2 |
| 60 | 0.30 - 0.42 | $1.05 - $1.47 | 6.0 - 8.4 |
| 120 (2 hours) | 0.60 - 0.84 | $2.10 - $2.94 | 12.0 - 16.8 |
There are a few exceptions. In extreme cold, idling for a minute or two allows oil to circulate before gentle driving. For hybrids, the gasoline engine may not even start during short stops. The best practice is to turn off your engine if you expect to be stopped for more than 60 seconds, except in traffic. This simple habit saves money and reduces engine wear.
