Should You Turn Off the Engine While Waiting in the Car?
3 Answers
If the waiting time is less than five minutes, you can keep the engine running; however, if it exceeds five minutes, it is advisable to turn off the engine. Otherwise, apart from wasting fuel and increasing engine carbon deposits, sitting in the car for an extended period while waiting not only consumes more fuel but also poses safety hazards. This is because the carbon monoxide content in car exhaust is extremely high. Prolonged idling while waiting can easily lead to carbon monoxide poisoning if not careful, especially in underground parking lots where it is crucial to avoid idling for too long. The hazards of prolonged idling are as follows: 1. Due to extended idling, the engine temperature remains too low, leading to incomplete fuel combustion, which can cause carbon buildup, clog the fuel injectors, and severe carbon deposits may even cause the piston rings to seize or break. 2. During prolonged idling, poor fuel atomization can result in unburned atomized diesel condensing and washing down the cylinder walls, entering the lubricating oil and diluting it, thereby accelerating engine wear as the moving parts do not receive adequate lubrication. 3. Poor combustion during prolonged idling worsens engine emissions. If toxic gases enter the cabin, occupants may face the risk of suffocation. Additionally, the release of toxic gases pollutes the environment. Some countries have traffic regulations that prohibit prolonged idling (limited to 3-5 minutes) when parking on the roadside, with fines enforced by traffic police for violations. 4. Low idle speed reduces the oil pump speed, leading to low oil pressure and insufficient lubrication at critical points. 5. While the engine maintains a constant internal operating temperature, components like the exhaust manifold and catalytic converter rely on airflow for cooling. Prolonged idling can hinder heat dissipation in high-temperature engine parts and may even damage the catalytic converter due to excessive heat. Generally, it is best not to let the engine idle for more than 10 minutes.
As a long-distance driver, whether to turn off the engine while waiting depends on how long the stop is. If it's just a minute or two, turning off and restarting the engine might actually consume more fuel due to the high fuel consumption during ignition. However, if the wait exceeds three minutes, I always turn off the engine. Many people might not know that idling not only burns fuel but also increases engine carbon deposits. Once, I idled for ten minutes without turning off the engine, and the next day, the engine shook badly. The mechanic said it was due to carbon buildup. The most frustrating situation is waiting with the air conditioning on in summer. I once idled for half an hour at the airport waiting to pick someone up, and the fuel gauge dropped rapidly—it was heartbreaking. Now, I bring a book and wait outside the car, saving fuel and protecting the car. Waiting for twenty minutes only consumes a few minutes' worth of fuel.
With a decade of auto repair experience, I recommend turning off the engine if idling exceeds 60 seconds. During idling, the engine maintains around 800 RPM. While it runs smoothly, insufficient fuel pump pressure can easily lead to clogged fuel injectors. Especially in winter when warming up the car while waiting, the white smoke is carbon particles from incomplete combustion. The most extreme case I've seen: a BMW owner idled for an hour daily waiting for their child at school, resulting in a $30,000 engine overhaul after six months. Modern cars with start-stop systems avoid this issue as the system automatically determines when to shut off. If concerned about starter wear, using genuine full-synthetic oil significantly reduces wear, allowing hundreds of start-stop cycles without problems.
