What happens if a car is left idling for 12 hours without turning off the engine?
2 Answers
Prolonged idling operation leads to excessively low engine temperature and incomplete fuel combustion, which can easily cause carbon deposits that clog fuel injectors. Severe carbon buildup may cause piston rings to seize or even break. Engines running at idle for extended periods exhibit poor combustion performance, resulting in deteriorated exhaust emissions containing toxic gases that pollute the environment. Therefore, some countries' traffic regulations prohibit any vehicle from prolonged idling operation (limited to 3-5 minutes) when parked roadside, with traffic police enforcing fines for violations. Poor fuel atomization causes unburned atomized diesel to condense, washing down cylinder walls and entering the lubricating oil, diluting and deteriorating the oil quality. This leads to insufficient lubrication for engine moving parts, accelerating engine wear.
I remember a time when a friend left his car idling in the yard all night, and in the morning, the engine was still running with the fuel gauge nearly empty. In such cases, it mainly wastes a lot of fuel—it’s not unusual for 12 hours to burn through most of a tank, especially with SUVs or older cars, which can be even more costly. Over time, this can lead to increased carbon buildup inside the engine due to incomplete combustion, potentially causing future issues like difficulty starting or rough acceleration. It also risks overheating components like the water pump or fan, and repairs for these can be expensive. I recommend developing a habit of turning off the engine or installing an automatic shutdown device—it’s safer and more convenient. In hot weather, an overheated engine could even ignite nearby flammable materials, which is quite dangerous.
