Which consumes more fuel: idling for 5 minutes or starting the engine?

[JoelLynn]

Idling consumes more fuel. Below is an introduction to idling: Introduction: Idling is an operating condition of a car, where the engine runs in neutral gear. Diagnosis of unstable idling: Uneven fuel injection or poor atomization from the injectors causes an imbalance in power output among the cylinders. If the oil pressure is too low, the fuel sprayed from the injectors may not atomize well or may spray in a line, and in severe cases, only droplets may be emitted, reducing the fuel injection amount and making the air-fuel mixture too lean. If the oil pressure is too high, the actual fuel injection amount increases, making the air-fuel mixture too rich. Faults in sensors or wiring can cause the control unit to issue incorrect commands, leading to improper fuel injection and resulting in an overly rich or lean air-fuel mixture, which is an indirect cause of unstable idling.

[HoldenFitz]

I've been driving for over a decade, so let me break this down clearly. Idling for 5 minutes definitely consumes more fuel! Think about it - once the engine starts, it's in working condition. Although the RPM is low, it's continuously burning fuel. Based on average idle fuel consumption, 5 minutes would waste roughly half a bowl of gasoline. While engine starting does cause a sudden surge in fuel injection, that only lasts a few seconds - the total fuel used would barely cover half a minute of idling. It's like boiling water: the initial flame flare-up consumes more gas, but keeping a small flame simmering wastes even more. The key factor is duration - if stopping for just a few minutes, it's better to turn off the engine to save fuel and reduce carbon buildup. Winter warm-ups are the exception though - proper idling is good for the car in cold weather.

[MacCharlie]

From a technical perspective, idling for 5 minutes consumes far more fuel than starting the engine. Although fuel consumption peaks during engine startup, it lasts for an extremely short duration—modern fuel-injected vehicles complete the process in about 0.5 seconds, consuming only around 5 milliliters of fuel. In contrast, idling consumes 15-30 milliliters per minute, totaling 75-150 milliliters over 5 minutes, which is over 15 times higher than startup fuel consumption. This is akin to comparing drinking from a large bucket versus sipping through a straw—starting the engine is like taking one big gulp, while idling is like continuously taking small sips that add up to more. Additionally, voltage impact should be noted: frequent starts can drain the battery, subsequently increasing fuel consumption. Therefore, it's recommended to maintain idling for stops under 1 minute.

[VanAurora]

Comparing these two scenarios, idling for 5 minutes clearly consumes significantly more fuel. Starting the engine uses a very small amount of fuel, just like striking a match to light a candle—once the match burns out, it's gone. However, when idling, the engine continues to run, consuming fuel every minute, and the accumulated amount over 5 minutes is substantial. Based on actual tests with my SUV, a cold start consumes about 0.03 liters of fuel, while idling for 5 minutes uses around 0.08 liters. Don’t be alarmed by the engine roar during startup—that’s not the main fuel consumer. Of course, in extremely cold regions, idling to warm up the engine is necessary, but modern cars only need about 1 minute of warm-up time; idling for 5 minutes is purely wasteful. Develop the habit: if you’re parked for more than 3 minutes, turn off the engine.