20 MPG combined isn’t going to win any awards for fuel frugality, and it’s certainly not the reason anyone buys a 2015 Mercedes-Benz SL550. This is a luxury roadster, a statement piece. This SL550 is for those who appreciate open-air motoring with a healthy dose of V8 power. For buyers of this car, fuel economy is a tertiary concern, far below the desirability of the badge, the intoxicating exhaust note, and the sun-drenched boulevard cruising experience.

City and highway performance

The EPA estimates for the 2015 SL550 are 18 MPG in the city and 24 MPG on the highway. While neither figure could be described as particularly impressive, they reflect the vehicle’s design. The 4.7L twin-turbocharged V8 is a powerful and refined engine, developing 429 horsepower. That kind of power requires fuel, and that’s evident in the city driving cycle. The highway figure improves as the engine settles into a more efficient cruising speed. The 7-speed automatic transmission helps in this regard, keeping the engine in its sweet spot for power and efficiency. But ultimately, physics prevail, and a nearly two-ton roadster simply isn’t as efficient as a smaller, lighter vehicle.

Annual fuel cost

The EPA calculates the annual fuel cost for the 2015 Mercedes-Benz SL550 at $2,900. This figure is based on driving 15,000 miles per year, using a national average for fuel prices. Keep in mind that this is just an estimate. Your actual fuel costs will depend on your individual driving habits, the price of gasoline in your area, and the grade of fuel you choose to use. The SL550 specifically requires premium fuel, which can drive up the cost.

Real-world expectations

While EPA estimates provide a useful benchmark, real-world fuel economy can vary significantly. Owners who primarily drive in stop-and-go city traffic should expect to see figures closer to, or even slightly below, the 18 MPG city estimate. Conversely, those who frequently undertake long highway journeys may achieve figures exceeding the 24 MPG highway estimate, especially if they employ a light foot and make use of the cruise control. Driving style and road conditions have a big impact on what each driver will experience.

How it compares

Compared to other luxury roadsters, the 2015 SL550’s fuel economy lands somewhere in the middle of the pack. For example, the BMW Z4 sDrive35i from the same year, equipped with a turbocharged inline-6, manages around 22 MPG combined. The Jaguar F-Type V6 S, with its supercharged six-cylinder engine, delivers almost identical numbers to the SL550. Going upmarket, you’ll find that vehicles like the Porsche 911 Carrera S Cabriolet often achieve slightly better fuel mileage, especially when equipped with the optional PDK transmission. For all Mercedes Benz fuel economy data, explore the FuelEconomyHub archives. Potential buyers should consider SL550 MPG across all years if historical data matters in the purchasing decision.

Tips to maximize efficiency

Take advantage of the SL550’s Eco driving mode. This mode alters the engine and transmission settings to prioritize fuel efficiency, resulting in smoother acceleration and earlier upshifts. While it may slightly reduce performance, it can make a noticeable difference in fuel consumption, particularly in city driving.

Ensure your tires are properly inflated to the recommended pressure. Underinflated tires increase rolling resistance, forcing the engine to work harder and consume more fuel. Check your tire pressures regularly, especially before long trips. A quality digital gauge helps to achieve consistency.

Reduce unnecessary weight. Carrying extra cargo in the trunk adds to the vehicle’s overall weight, impacting fuel economy. Remove any unnecessary items from the car to minimize the load on the engine. This practice is especially important with a vehicle prone to aggressive driving and acceleration.

Practice smooth and consistent driving habits. Avoid sudden acceleration and hard braking, as these actions consume more fuel. Anticipate traffic flow and maintain a steady speed whenever possible. Gradual acceleration is almost always the better approach.

Consider the grade of fuel you’re using. The SL550 requires premium fuel. Using a lower octane grade may not immediately damage the engine, but it can reduce performance and, potentially, decrease fuel economy over time as the engine management system compensates. Following manufacturer recommendations ensures optimal engine performance and efficiency.