Is it serious if the car is left running all night?
3 Answers
Forgetting to turn off the engine once or twice is not a big problem, but if this happens frequently, it will definitely cause damage to the car, especially if the car is left running all night. Here is more relevant information: 1. Carbon deposits: In idle state, the car will keep injecting fuel. Since the car remains in idle for a long time, the air intake is very small. On one hand, this prevents the cleaning of the intake tract and related parts, and on the other hand, it also leads to insufficient oxygen, making it easier for incomplete combustion to occur, thus easily causing carbon deposits. 2. Increased engine wear: Leaving the engine running all night will prolong the idle time, reduce the oil pump speed, and result in lower oil pressure, making it difficult to effectively lubricate parts such as the bearing bushes. This will increase wear on the piston, connecting rod, and engine. 3. Fuel consumption: Forgetting to turn off the engine keeps the car in idle state, continuously consuming fuel. Under idle conditions, fuel consumption is obviously higher than at economical speeds. If the fuel level is already low, the vehicle may stop working immediately, directly increasing the average fuel consumption of the car.
Last time I returned from a business trip, I noticed that BMW in our neighborhood had been left idling all night with water droplets dripping from the exhaust. The most immediate consequence of this situation is a spike in fuel consumption—typically, idling for an hour can burn 4-8 liters of gasoline, equivalent to wasting over half a tank. The bigger issue is carbon buildup. At low temperatures and low RPMs, incomplete fuel combustion leads to sticky deposits forming on the spark plugs and the back of the valves. My mechanic buddy, Lao Zhang, says the best remedy in such cases is to take the car for a high-speed run to flush out the internals at higher RPMs. In southern summers, overheating becomes another concern—like that car in our underground garage whose cooling fan failed due to prolonged idling. Of course, the most dangerous scenario is in enclosed garage spaces. A friend’s company car once had a close call with carbon monoxide seeping back into the cabin.
Last time my neighbor left their Sagitar idling overnight without turning off the engine, and the next day they saw the fuel gauge needle had dropped to the bottom. This situation is actually quite damaging to the car, especially to the engine and emission system. When idling, the cylinder temperature is relatively low, and gasoline combustion efficiency is poor, which easily leads to the formation of black carbon deposits around the fuel injectors. Over time, this can cause difficulties during cold starts and abnormal increases in fuel consumption. Additionally, the catalytic converter is also affected. The converter needs to operate at high temperatures, and prolonged idling at low temperatures can cause coking on its surface. My old Accord had to have its catalytic converter replaced because of this issue, costing several thousand yuan. I recommend everyone take an extra glance at the tachometer after parking or install a mobile app with vibration alerts.
