Does Idling Waste Fuel?

[GarrettLee]

Idling does waste fuel. Below are the reasons why idling consumes fuel: Carbon Buildup Wastes Fuel: Idling not only wastes fuel but also harms the vehicle. The engine's valves and pistons will accumulate significant carbon deposits, which are difficult to remove unless the cylinder head is opened. This leads to rapid engine aging. Therefore, unless at a traffic light, it is generally advisable to turn off the engine when parked. Engine Operation Consumes Fuel: The engine continues to supply fuel, and the fuel injectors remain active. For prolonged idling periods (except when using air conditioning), it is recommended to shut off the engine. At the engine's economic speed (torque point), a higher proportion of fuel is converted into useful work, whereas at low speeds (below 1000 RPM) or high speeds, the conversion efficiency drops (by 10%-20%).

[CassandraLee]

I recently looked into this matter, and it's true that idling does consume fuel. As long as the engine is running, it needs fuel to maintain its RPM. I conducted a test with my own 1.6L sedan: with the AC on and idling for an hour, the fuel gauge dropped by about 1.5 liters. Once, while waiting for someone for thirty minutes, I could practically feel my wallet getting lighter. However, for short durations like under two minutes, turning the engine off and restarting it actually consumes more fuel—the fuel used in a cold start is equivalent to idling for over ten seconds. This is why many new cars come with auto start-stop features that shut off the engine automatically after thirty seconds. My advice? If you're stuck in traffic for more than a minute, manually turn off the engine—the fuel savings could buy you a bubble tea.

[McSamantha]

My decade-old SUV has turned me into an idle fuel consumption expert. Once, while picking up my kid from school, I got stuck at the gate for half an hour in idle mode—the fuel gauge dropped two bars, and the dashboard showed average fuel consumption soaring to 18L/100km. Later, I bought an OBD scanner to check the data: this 2.4L engine injects 40-50ml of fuel per minute at idle. That translates to at least 2.4 liters per hour, burning half a dime every second. And if the AC is on, the compressor adds an extra 15% load on the engine. So now I’ve made it a habit—if I expect to stop for more than 90 seconds, I turn off the engine. Saves money and reduces carbon buildup.

[LaLilah]

I remember my driving instructor saying that idling the engine is like burning money for fun. Last time I was waiting for someone in the car with the heater on during a camping trip at night, I burned through a quarter tank of gas in two hours – you could literally watch the fuel gauge needle drop. The mechanic told me idle fuel consumption is directly linked to engine displacement: small-displacement cars use 1-2 liters per hour, while large-displacement engines can consume up to 4 liters. Now with summer here and AC usage increasing, the moment the compressor kicks in, instantaneous fuel consumption can spike to 3L/h. Practical tests show hybrid cars with auto start-stop are most efficient, as the AC runs on battery when the engine shuts off. Recommendation: turn off the engine if parked for over three minutes – the fuel saved could get you another 10km down the road.