Does an automatic transmission car consume more fuel the slower it drives?

[CamilleLee]

An automatic transmission car does not necessarily consume more fuel the slower it drives. Whether a car saves fuel or consumes more depends on road conditions, load, and speed. Driving slowly does not always mean saving fuel, and driving fast does not always mean consuming more fuel. Here are some precautions for driving an automatic transmission car: 1. Gear shifting: Generally, you do not need to press the shift button when switching between N, D, and 3. However, when shifting from 3 to lower restricted gears, you must press the shift button. Shifting from lower to higher gears does not require pressing the shift button. 2. Driving process: Never shift into N gear while driving to coast, because the automatic transmission requires lubrication. When the gear is placed in N while driving, the oil pump cannot supply oil normally for lubrication, which will increase the temperature of internal transmission components and cause complete damage. 3. Temporary parking: For example, when waiting at a red light, either N or D is fine, depending on your habit. If the parking time exceeds half a minute, you should shift into N and apply the handbrake.

[MacCecilia]

Having driven automatic transmission cars for over a decade, I genuinely believe driving too slowly actually consumes more fuel. Back when I was crawling in city traffic at low speeds, my fuel consumption could skyrocket to over 12 liters per 100km. Later, when I maintained a steady 60-70 km/h on national highways, it dropped to 8 liters. It's like how running is faster than walking but consumes more energy – at low speeds, the engine has to work continuously without covering much distance. This is especially true now that many cars have auto start-stop systems; the frequent battery operation during repeated starts actually increases fuel consumption. My advice is to avoid peak congestion hours and maintain moderate speeds – it's friendlier to both your wallet and the environment.

[DeCharles]

From a vehicle engineering perspective, the high fuel consumption at low speeds in automatic transmissions is primarily related to transmission logic. At 20 km/h, the vehicle typically gets stuck in low gear, causing the engine RPM to soar while output efficiency remains low, wasting fuel as heat. When speed increases to around 60 km/h, the transmission intelligently shifts to higher gears, stabilizing RPM and ensuring complete combustion. I've observed with an OBD scanner that instantaneous fuel consumption is 12L/100km at 30 km/h, but immediately drops to 7L when reaching 60 km/h. Additionally, low-speed driving during cold starts consumes the most fuel, as the catalytic converter hasn't reached operating temperature yet.

[Hope]

Every automatic transmission car has an optimal fuel-saving speed, and my experience is to monitor the engine RPM. The most economical fuel consumption occurs when the RPM stabilizes at 1500, which typically corresponds to a speed of 60-80 km/h. Below 40 km/h, the RPM drops below 1000, leading to incomplete combustion in the cylinders and gasoline utilization of less than 30%. Once, I specifically tested this by driving at a constant speed of 70 km/h in fuel-saving mode with cruise control, saving 3 liters of fuel compared to my friend driving the same route at 40 km/h. In fact, driving over 100 km/h on highways also consumes more fuel, mainly due to high wind resistance, so maintaining a moderate speed is the most cost-effective.