What Uses More Gas: Neutral or Engine Braking When Going Downhill?

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Engineering Explained hits the road to find out which method – neutral or engine braking – is more fuel efficient. Which one do you use when you drive your Mustang down hills?

There are two major ways you can go down a hill in your Mustang: pop it into neutral and coast or let the engine do the braking for you. If you happen to live in an area with several elevation changes, you probably have a tried-and-true method. Which one uses the least amount of gas, though?

Engineering Explained‘s Jason Fenske wanted to find the answer to that question, so he made the above video. He just focuses on maximum fuel economy for a modern, fuel-injected car, not whether or not one approach is safer or better for your brakes, etc.

 

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The simple answer to the question is…there is no simple answer. It depends on your circumstances.

If you’re just going from the top of a hill and straight to the bottom, it’s better to use engine braking to slow you down. Leaving your car in gear and taking your right foot off of the throttle means the fuel injectors are not operating. The free forces of physics get you to your destination, not costly fuel. Using neutral in that situation would cause the engine to idle, which requires gas.

If you’re driving down a hill, then up a short incline, then going downhill and up another incline, it’s more fuel efficient to just leave your car in neutral. That allows it to build more speed during the descent, which it can then use to power up the hill. You are using a little gas, but momentum is doing most of the work for you. Think of it like a rollercoaster. And think of just exactly how you’re slowing down the next time you go downhill in your Mustang.

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Derek Shiekhi contributes to a variety of Internet Brands’ Auto sites, including J-K Forum , Jaguar Forums, and 5 Series. He's also a member of the Texas Auto Writers Association.

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