The 2021 Mercedes-AMG GLS 63 mpg test: The test nobody really needs to know but we’re still doing. There once was a day someone in the automotive market was dreaming for a seven-seat SUV that can hit 60 miles per hour in less than four seconds. Well, dream no more! Today, unbelievably, there is a product available that meets those criteria. The Mercedes-AMG GLS 63 is the 603 horsepower three-row monster that no consumer has need for. It’ll do 0-60 in 3.6 seconds and makes about the same torque as most diesel one-ton trucks were making not long ago. Yes, 2008 is not that long ago; fight me.
After our highway-fuel-economy test of this loaded baby-hauler, we found it still returned about 22 mpg. This is really not that bad considering its weight and power and that the EPA’s highway estimate is only 18. Surprisingly, the new Mercedes-Maybach GLS 600 is rated at 19.
If you were to hyper-mile this guy from tank to tank, our test number multiplied by this behemoth’s 23.8 fuel capacity would give your calculator about 520 miles before you were subjugated to the side of the road. Chances are your spirited acceleration onto the highway to hear the Mercedes-AMG M177 roar would take it down to much less.
How We Test
This Daily Motor 2021 Mercedes-AMG GLS 63 mpg real-world highway fuel economy test consists of over 100 miles of consistent highway driving. We fill the car using the “three-click method,” meaning running the gas pump on high flow until it clicks, waiting ten seconds, running low flow until it clicks again, waiting another ten seconds, then running low flow one very last time. The lowest-octane gasoline accepted by the vehicle’s manufacturer is used. We then drive about fifty miles on public highway in one direction and then back in the opposite direction, attempting not to draft or drive aggressively. We set the cruise control at GPS-indicated 72 mph in an attempt to achieve a moving average speed of 70 mph over the entire test. Upon return to the gas station, we refill at the same fuel pump as the initial fill using the same fueling method. Miles per gallon is determined by dividing total miles traveled by fuel used. In cases where our observed figure differs greatly from the vehicle’s indicated figure and/or EPA’s estimate, we may recommend a number in between or plan to retest the vehicle.
Watch the 2021 Mercedes-AMG GLS63 mpg test here: