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Video | I Ran The 603 Horsepower Mercedes-AMG GLS 63 Out of Gas

Earlier this fall I had a chance to review the 2021 Mercedes-AMG GLS 63.  The GLS is Mercedes’ largest SUV, and the third-generation model came out for the 2020 model year.  It was known as the GL until halfway through its previous generation when it was given the GLS name in line with a re-shuffling of Mercedes’ nomenclature.  Its main selling point is its standard three rows of seats, making it the company’s de-facto family hauler, though in upper trims it becomes more of a high-riding SUV version of the S-Class full-size sedan.  The GLS I was driving was the high-performance AMG GLS 63 model, which joins the lineup as a 2021 model.  It packs a twin-turbo 4.0-liter V8 engine supplemented by a 48-volt mild hybrid system.  Output is 603 horsepower and 627 lb-ft of torque. 0-60 comes in 4.1 seconds according to Mercedes-Benz, though I clocked the vehicle myself at 4.6 seconds in the parking lot of an empty warehouse using the onboard 0-60 timer.  Keep in mind this thing weighs 5,754lbs.

Despite its incredibly posh cabin (heated front armrests; three heated and chilled cup holders; a pop-out android tablet in the second row, four massaging seats) this ridiculous performance is what I enjoyed most about the GLS.  I drove it a lot over the course of my loan, to the point where when I set out to actually record a video with it on the last day of my load, it was sitting on about 41 miles of range left in the tank.

Mathematically, this was more than I should’ve needed for the driving route I use for my ‘performance car’ reviews, which covers about 23 miles round trip. What I failed to consider though is that the GLS’s remaining range had been calculated based on the 20 mpg average I had returned over the course of my loan, which included a 300-mile highway road trip.  As I would learn next, the GLS 63 achieves considerably less than 20 miles per gallon when you’re driving it… spiritedly.  Thanks to Sport+ mode, a few stop light acceleration demos, and the allure of the 80 mph winding canyon roads between Salt Lake City and Park City, I would burn through every drop of this 41 miles of range over the next 11.4 miles, which works out to 5.6 miles per gallon.  

The tank went dry shortly after I’d finished raving into my camera about the physics-bending performance of the GLS 63, so I was able catch it all on video.  Basically, the check engine light came on and the car began to sputter; luckily I had enough momentum remaining to pull off to the side of the road, where the vehicle would take one last gasp of the remaining fumes in the tank, and then die.  Once I came to terms with the fact that I’d run it dry, which I'll admit took me a few minutes, I used the little Mercedes roadside assistance button on the overhead console to call for help; the first time I’d ever pressed one of these buttons on purpose.  The Mercedes customer service associate couldn't have been more helpful, and helped me to make light of the situation.  He was also able to locate my exact location on a map; I only had to confirm whether I was traveling eastbound or westbound.  A third-party roadside serviceperson was called upon to bring me a few gallons of gas.  I received a text from Mercedes roadside with a link to a web app that shows you the driver’s location. In my case though, the driver's location turned out to be way off, and when it said the driver was five minutes away, he called me to tell me he’d be to me in half an hour.  Ultimately, I sat on the side of the highway for about an hour and a half; it was funny at first... then the sun went down.  A little more than an hour in, the car gave a ‘low battery’ warning light, and I opted to shut off the auxiliary power to avoid a dead battery.  Roadside assistance arrived after some time and added some fuel to the GLS’s tank without me even needing to get out of the car.  It was more than enough to get me home, but I still stopped at a gas station a mile up the road.  Arriving home after the whole ordeal was the first time I’ve ever been happy to get out of the driver’s seat of a 600 horsepower car. Find a Mercedes-Benz GLS 63 for sale

Chris O'Neill grew up in the rust belt and now lives in Salt Lake City, Utah. He worked in the auto industry for a while, helping Germans design cars for Americans. On Instagram, he is the @MountainWestCarSpotter.


Chris O'Neill
Chris O'Neill
Chris O'Neill is an author specializing in competitive analysis, consumer recommendations, and adventure-driven enthusiast content. A lifelong car enthusiast, he worked in the auto industry for a bit, helping Germans design cars for Americans, and now lives in Salt Lake City, Utah. He runs an Instagram account, @MountainWestCarSpotter, which in his own words is "actually pretty good", and has a... Read More about Chris O'Neill

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