The 2020 Mercedes-Benz SL450, with its 3.0L inline-six and a combined EPA rating of 22 MPG, isn’t trying to deliver economy car numbers, and it shouldn’t. This is a grand touring roadster designed for effortless cruising and spirited backroad drives. The customer this car targets prioritizes refinement, performance, and open-air thrills over maximizing miles from a gallon of premium fuel.

City and highway performance

The SL450’s official EPA ratings are 20 MPG in the city and 28 MPG on the highway. The city number reflects stop-and-go traffic, where the engine’s start/stop system and the nine-speed automatic transmission work to minimize fuel consumption. On the open road, the 28 MPG figure is more relevant, showing reasonable efficiency for long-distance journeys, especially considering the car’s performance capability. Keep in mind that aggressive driving will significantly decrease these numbers. The SL 450’s powertrain delivers smooth and responsive power, and using that power comes at a cost.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2020 Mercedes-Benz SL450 will be $2,650. This is based on driving 15,000 miles per year and using current national average fuel prices for premium gasoline. Your actual fuel costs may vary depending on your driving habits, the type of driving you do, and the price of gasoline in your area. The $2,650 provides a good benchmark for understanding the SL450’s fuel expenses.

Real-world expectations

The SL450’s official MPG figures represent a laboratory-controlled ideal. Your personal MPG will change based on driving style, traffic conditions, and environmental factors like temperature and wind. Owners who frequently use the engine’s power will likely see numbers below the EPA estimates, especially in the city. However, those who drive smoothly and consistently on the highway can likely achieve numbers closer to the 28 MPG rating. Across all model years, the SL450 MPG generally stays in this range, reflecting a consistent focus on performance over economy.

How it compares

In the world of luxury roadsters, the SL450’s fuel economy is roughly in the middle. The BMW Z4 M40i, with its similar inline-six turbo engine, gets a slightly better 25 MPG combined. The Porsche 718 Boxster S, while offering a thrilling driving experience, gets around 22 MPG combined, matching the SL450’s rating. Audi’s TT Roadster, with its smaller four-cylinder engine, manages a more frugal 26 MPG combined. The SL450 buyer weighs these slight MPG differences against the car’s luxury, performance, and brand value when deciding where to spend their money. Don’t forget to browse all Mercedes Benz fuel economy data when weighing your options.

Tips to maximize efficiency

Use the “Eco” mode. This setting will remap the throttle response and shift points, prioritizing fuel efficiency over acceleration. It won’t transform the SL450 into a hybrid, but it can improve MPG during everyday driving.

Keep proper tire inflation. Underinflated tires increase rolling resistance, forcing the engine to work harder and consume more fuel. Check your tire pressures regularly and inflate them to the recommended levels found on the driver’s side doorjamb.

Anticipate traffic flow. Avoid sudden acceleration and braking by looking ahead and maintaining a consistent speed whenever possible. Smooth driving is more fuel-efficient driving, and helps you stay closer to that 28 MPG highway number.

Minimize idling. The SL450 features an automatic start/stop system that shuts off the engine when you come to a complete stop and restarts it when you lift your foot off the brake pedal. Let it do its job because it can reduce fuel consumption in stop-and-go traffic.