The 2015 Mercedes-Benz SLK350 offers stylish, open-top motoring, but it comes at the cost of 24 MPG combined. This isn’t a hybrid, and it makes no such claims. Instead, it’s a precisely engineered roadster with a sonorous V6, aimed at those who prioritize driving pleasure over fuel efficiency. SLK350 buyers understand they’re paying a premium for the experience: the responsive engine, the handling, and the sheer curb appeal that comes with the Mercedes-Benz badge.

City and highway performance

The SLK350 gets 21 MPG in the city and 28 MPG on the highway. The city number shows how the engine has to work harder in stop-and-go traffic, using the automatic transmission’s lower gears to stay responsive. But, the highway figure is a sweet spot, showing how efficiently the car can cruise when the engine settles into its higher gears. The 7-speed automatic transmission is important here, allowing for relaxed highway speeds with the engine barely ticking over.

Annual fuel cost

The EPA estimates the annual fuel cost for the 2015 Mercedes-Benz SLK350 at $2,400. This is based on driving 15,000 miles per year, with a mix of city and highway driving, using the national average fuel price. Of course, individual fuel costs will vary based on driving habits and local fuel prices. However, the $2,400 figure gives potential owners a benchmark to consider and compare with other vehicles in its class.

Real-world expectations

The EPA’s figures are a good starting point, but real-world fuel economy often changes based on driving style and conditions. Drivers with a heavier foot or who primarily drive in congested urban areas might see figures closer to the city estimate. However, drivers who primarily use the SLK350 for longer highway journeys, and who practice smooth acceleration and maintain consistent speeds, could realistically get better fuel economy than the official highway figure. The V6’s sound might tempt some into more spirited driving, lowering MPG.

How it compares

The SLK350 is in the middle of its class regarding fuel economy. For instance, the BMW Z4 sDrive35i, with its turbocharged inline-6, gets roughly similar fuel economy numbers. The Porsche Boxster, depending on configuration, might offer slightly better fuel economy. The base model with its smaller engine gets around 22 MPG combined. The SLK350 stands out with its retractable hardtop, making it suitable year-round, which appeals to buyers in colder climates who might not consider a soft-top-only Boxster. All Mercedes Benz fuel economy data can be viewed online to make a holistic comparison. See the SLK350 MPG across all years to see trends over the years.

Tips to maximize efficiency

On highway drives, use cruise control. Keeping a consistent speed reduces driver fatigue and helps the engine run most efficiently. Gradual acceleration and avoiding sudden bursts of speed can also save fuel. The V6 might tempt you to enjoy the power, but being light on the accelerator will reduce gas consumption.

Make sure your tires are properly inflated. Underinflated tires increase rolling resistance, making the engine work harder and reducing fuel economy. Check your tire pressure regularly and inflate them to the recommended pressure, usually on a sticker inside the driver’s side doorjamb. This is especially useful on a roadster like the SLK, where tire pressure can significantly affect handling.

Maintain routine maintenance. Regular oil changes, air filter replacements, and spark plug maintenance ensure that the engine runs at peak efficiency. A well-maintained engine is a fuel-efficient engine. See the Mercedes-Benz service schedule for recommended intervals.

Reduce extra weight in the vehicle. Extra cargo adds weight, requiring the engine to work harder, which impacts fuel economy. Remove any unnecessary items from the trunk or passenger compartment. Every bit helps.

Use the highest gear possible. In manual mode, upshift early. The SLK350’s engine has enough torque to pull strongly even at lower RPMs. Running the engine in a higher gear at lower RPMs reduces fuel consumption. The 7-speed automatic transmission was designed for this purpose, so let it do its job.