23 MPG combined isn’t going to win any awards, but for the 2018 Mercedes-Benz SL450, it’s arguably acceptable. This isn’t a car bought for its fuel efficiency; it’s a luxurious grand tourer, designed for effortless open-road cruising and a refined top-down experience. The SL450 buyer prioritizes performance, prestige, and comfort over squeezing every last mile from a gallon of premium fuel.

City and highway performance

The EPA estimates the SL450 achieves 20 MPG in the city and 28 MPG on the highway. The city figure reflects the realities of stop-and-go traffic, where the 3.0L turbocharged six-cylinder engine works harder. However, once you’re out on the open road, the nine-speed automatic transmission can settle into its higher gears, allowing for relaxed cruising and improved fuel economy. That 28 MPG highway rating is achievable, but only with a light foot and a consistent speed. Push the car harder, and that number will quickly decrease.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2018 Mercedes-Benz SL450 at $2,500. This is based on driving 15,000 miles per year and using national average fuel prices. This figure serves as a helpful benchmark, but individual fuel costs will vary depending on driving habits, local fuel prices, and the type of fuel used. Remember, the SL450 requires premium gasoline, which is typically more expensive than regular unleaded.

Real-world expectations

While the EPA figures provide a baseline, real-world fuel economy often differs. Expect the SL450 to deliver slightly lower than the stated 23 MPG combined in mixed driving. Factors such as aggressive acceleration, frequent short trips, and using the air conditioning can all negatively impact fuel economy. On the other hand, consistent highway driving at moderate speeds might yield slightly better results. It’s crucial to monitor your own driving habits to get a more accurate understanding of your SL450’s fuel consumption. A lead foot will easily drop you into the high teens while gentle cruising can get you closer to, or even slightly above, the EPA estimates.

How it compares

The SL450’s fuel economy is reasonably competitive within its class. The BMW 840i Convertible, for example, with its 3.0L inline-six, achieves EPA-estimated ratings of 23 MPG combined, 20 MPG city, and 29 MPG highway, very close to the SL450. An Audi S5 Cabriolet with its turbocharged V6 manages around 24 MPG combined. The Porsche 911 Carrera Cabriolet, despite its sporting pretensions, can achieve a respectable 20 MPG city and 27 MPG highway, though many owners of that vehicle likely aren’t thinking about fuel efficiency. All Mercedes Benz fuel economy data is available online. The SL450 buyer likely cross-shops these vehicles based on brand preference, styling, and performance characteristics, with fuel economy playing a secondary role. For detailed information about SL450 MPG across all years, you can find data here.

Tips to maximize efficiency

Optimize your driving style by avoiding aggressive acceleration and hard braking. The SL450’s twin-turbo V6 delivers ample power throughout the rev range, so there’s no need to constantly push it to the redline. Smooth, gradual acceleration will significantly reduce fuel consumption.

Ensure your tires are properly inflated. Underinflated tires increase rolling resistance, which forces the engine to work harder and consume more fuel. Check your tire pressures regularly and maintain them at the recommended levels, typically found on a sticker inside the driver’s side door or in the owner’s manual.

Minimize unnecessary weight. Carrying extra cargo in the trunk reduces fuel economy. Remove any items that you don’t need to carry regularly, as every extra pound adds to the vehicle’s overall weight and increases fuel consumption.

Use cruise control on the highway. Maintaining a consistent speed helps to optimize fuel efficiency. Cruise control allows the engine to operate more smoothly and efficiently, especially on long stretches of open road.

Consider using the ECO driving mode, if equipped. This mode typically adjusts throttle response and shift patterns to prioritize fuel economy. While it may slightly reduce performance, it can make a noticeable difference in fuel consumption, particularly during city driving.