20 MPG combined is not the reason anyone buys a 2018 Mercedes-Benz SL550. They buy it for effortless V8 power, a disappearing hardtop, and the three-pointed star on the hood. Fuel economy registers somewhere far below those priorities, more like a background hum than a deal-breaker. This is a grand touring machine, designed for covering vast distances in comfort and style, and the fuel consumption is a consequence, not a core attribute.

City and highway performance

The EPA estimates for the 2018 SL550 are 17 MPG in the city and 25 MPG on the highway. The city number reflects the realities of stop-and-go driving, where the 4.7L twin-turbocharged V8 is constantly asked to accelerate the car’s considerable weight. The 25 MPG highway figure, while achievable, is contingent on a light foot and steady cruising. Push the pace, exploit the engine’s abundant power for overtaking, and expect that number to drop. The nine-speed automatic transmission certainly helps keep the engine in its sweet spot, but it is still a powerful V8. People considering the SL550 MPG across all years need to consider how often they prioritize a spirited drive, as that will greatly affect their average fuel consumption.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2018 Mercedes-Benz SL550 at $2,900. This figure is based on driving 15,000 miles per year and using national average fuel prices. It’s important to remember that this is just an estimate. Actual fuel costs will vary depending on driving habits, local fuel prices, and the grade of fuel used. The SL550 requires premium fuel, which typically commands a higher price than regular gasoline; factoring this in is key to having realistic expectations. Someone who drives primarily in the city and enjoys rapid acceleration will likely exceed the $2,900 estimate considerably. Those who spend more time on the highway and drive conservatively may come in under it.

Real-world expectations

Expect to see figures hovering around the EPA estimates, but possibly slightly lower depending on your typical driving environment. Short trips, frequent cold starts, and aggressive driving will all negatively impact fuel economy. This is a car that rewards smooth, deliberate inputs, especially when trying to conserve fuel. Keep in mind that the SL550 is a performance car first and foremost. While the nine-speed automatic helps, the expectation of hybrid-like fuel economy is unrealistic.

How it compares

Compared to other high-performance roadsters, the SL550’s fuel economy is generally in line with its competitors. The BMW Z4 M40i, while featuring a smaller inline-six engine, delivers around 25 MPG combined. The Porsche 911 Carrera Cabriolet, with its turbocharged flat-six, manages around 20 MPG combined, similar to the SL550. The Jaguar F-Type R Convertible, with its supercharged V8, typically achieves slightly lower fuel economy, around 18 MPG combined. The Porsche is more driver-focused, the BMW is more sporty, and the Jaguar has a more aggressive sound, but the Mercedes balances its luxury and performance credentials nicely, a sweet spot appealing to its clientele. See all Mercedes Benz fuel economy data for comparison to other models in their lineup.

Tips to maximize efficiency

Gentle acceleration is your friend. Avoid stomping on the gas pedal unless absolutely necessary. The SL550 has more than enough power to get up to speed without needing to constantly engage the turbos. The engine produces its torque low-down, meaning less fuel is needed at city speeds.

Use cruise control on the highway to maintain a consistent speed and avoid unnecessary fluctuations in throttle input. Consider using the “Comfort” driving mode, which optimizes the car’s settings for fuel efficiency and relaxed driving. In Sport mode, it may feel fun to enjoy the car’s speed, but your MPG will suffer.

Maintain proper tire inflation. Under-inflated tires increase rolling resistance, which negatively impacts fuel economy. Check your tire pressures regularly and inflate them to the recommended levels. Keeping the tires properly maintained will help you in all areas of the car’s performance, from cornering to efficiency.

Reduce unnecessary weight in the car. Carrying extra weight reduces fuel economy, so remove any unnecessary items from the trunk and passenger compartment. Think about that set of golf clubs you keep in the trunk “just in case.”

Consider turning the engine off during longer stops. Start-stop is standard on the vehicle and can dramatically reduce fuel consumption at red lights. While it may be jarring at first to see the engine shut off, it is one of the most significant upgrades in gas mileage in current vehicles.