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.
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's father raised him on cars. As a boy, Derek accompanied his dad as he bought classics such as post-WWII GM trucks and early Ford Mustang convertibles.
After loving cars for years and getting a bachelor's degree in Business Management, Derek decided to get an associate degree in journalism. His networking put him in contact with the editor of the Austin-American Statesman newspaper, who hired him to write freelance about automotive culture and events in Austin, Texas in 2013. One particular story led to him getting a certificate for learning the foundations of road racing.
While watching TV with his parents one fateful evening, he saw a commercial that changed his life. In it, Jeep touted the Wrangler as the Texas Auto Writers Association's "SUV of Texas." Derek knew he had to join the organization if he was going to advance as an automotive writer. He joined the Texas Auto Writers Association (TAWA) in 2014 and was fortunate to meet several nice people who connected him to the representatives of several automakers and the people who could give him access to press vehicles (the first one he ever got the keys to was a Lexus LX 570). He's now a regular at TAWA's two main events: the Texas Auto Roundup in the spring and the Texas Truck Rodeo in the fall.
Over the past several years, Derek has learned how to drive off-road in various four-wheel-drive SUVs (he even camped out for two nights in a Land Rover), and driven around various tracks in hot hatches, muscle cars, and exotics. Several of his pieces, including his article about the 2015 Ford F-150 being crowned TAWA's 2014 "Truck of Texas" and his review of the Alfa Romeo 4C Spider, have won awards in TAWA's annual Excellence in Craft Competition. Last year, his JK Forum profile of Wagonmaster, a business that restores Jeep Wagoneers, won prizes in TAWA’s signature writing contest and its pickup- and SUV-focused Texas Truck Invitational.
