Coasting in ‘neutral’ actually burns more gas than ‘drive’
Like most stubborn urban legends, coasting in neutral to save gas makes intuitive sense. When you shift your car into neutral, your engine spins down to its lowest possible RPM. So if you’re coasting down a long hill, you might as well shift your transmission into neutral, let gravity propel your car, and save some gas. Right? Wrong.
According to Mike Allen at Popular Mechanics, a modern car with an automatic transmission will burn more fuel coasting in neutral than it will coasting in drive. Confusing? There’s a reason.
Why coasting in neutral will burn more gas than leaving your car in drive
If your car is sitting still, and doesn’t have automatic engine start/stop, and you shift into neutral, then it will idle down to its minimum RPM. What’s the minimum RPM? The speed the engine must continue turning to spin its own oil pump and water pump so it doesn’t overheat and blow up. Idling like this, most engines will burn through approximately one gallon of gasoline per hour.
Let’s say you’re coasting down a long hill and shift your automatic transmission into neutral. The same thing will happen.
A modern car coasting down a hill in drive will burn less than one gallon per hour. Why? It shuts off fuel flow to the engine because it knows gravity will keep spinning the motor over, and thus spinning the oil and water pump. That’s right—coasting downhill in drive, you’re already not burning any gasoline.
Allen has actually tested this exact scenario, measuring the electricity flowing into the fuel injectors while coasting in drive. Sure enough, the engine isn’t injecting any fuel into the cylinders.
The long and short of it is that automakers are under such EPA pressure to improve fleet gas mileage, they’ve rung every last percentage point of efficiency possible out of the internal combustion engine.
Perhaps an old manual transmission car with the clutch pedal pressed will use less gasoline. But a modern car is a fuel-saving machine, and you probably won’t outsmart the folks who engineered it with urban legend driving advice—even if it makes intuitive sense. In addition, coasting while driving is dangerous and illegal.
You can see the Discover channels Mythbusters take on more hyper-miling methods in the video embedded below:
