The official figure is what a Mercedes-Benz sl managed in a laboratory. These are the figures owners report from the road, engine by engine, for every generation we hold. Add your own at the bottom and the averages get better for the next buyer.
| Engine | Official (NEDC) | Official (WLTP) | Real MPG | % of official | Owners report |
|---|---|---|---|---|---|
| SL 300 | 30.4 | – | 26.4 | 87% | – |
| SL 350 | 29.1 | – | 26.2 | 90% | 23.8–29.0 |
| SL 500 | 24.4 | – | 23.7 | 97% | 20.0–27.0 |
| SL 600 | 20.3 | – | – | – | – |
| SL 63 AMG | 20.0 | – | 19.5 | 98% | 19.0–20.0 |
| SL 65 AMG | 20.2 | – | 17.9 | 88% | 14.7–21.0 |
| SL55 AMG | 19.3 | – | 18.3 | 95% | 13.9–21.3 |
| Engine | Official (NEDC) | Official (WLTP) | Real MPG | % of official | Owners report |
|---|---|---|---|---|---|
| SL 350 | 37.7–39.2 | – | 32.7 | 85% | 27.0–36.6 |
| SL 400 | 33.6–36.7 | 28.8 | 31.5 | 109%* | – |
| SL 400 Mille Miglia | 36.7 | – | – | – | – |
| SL 500 | 28.8–31.0 | 26.4 | 25.6 | 97%* | – |
| SL 500 Mille Miglia | 31.0 | – | – | – | – |
| SL 63 AMG | 24.1–28.8 | – | 18.5 | 70% | 18.0–19.0 |
| SL 65 AMG | 23.7–24.4 | – | – | – | – |
| Engine | Official (NEDC) | Official (WLTP) | Real MPG | % of official | Owners report |
|---|---|---|---|---|---|
| SL 43 | – | 30.1 | – | – | – |
| SL 55 | – | 21.9 | – | – | – |
| SL 63 | – | 21.9 | – | – | – |
All figures in miles per gallon (UK). “Owners report” is the spread of individual submissions for that engine. * Measured against the WLTP figure rather than NEDC.
What does yours actually do? Read it off the trip computer over a full tank or work it out from litres and miles. No postcode, no sign-up. The more people add, the better the averages get, and this page stays free.
Owners report an average of 26.6 mpg across all Mercedes-Benz sl engines with data, about 92% of the official combined figure. The engine tables on this page give the figure for each engine and generation.
Official figures come from a laboratory test cycle, not the road. Cold starts, short trips, hills, load, tyres and driving style all cost fuel the test does not see. A gap of 10 to 30 per cent is normal; a much bigger gap on one engine usually points at a fault, a heavy right foot, or a diesel that never gets warm.
Honest John closed in August 2026 and its Real MPG section went with it. This page is where the Mercedes-Benz sl figures now live: rebuilt from the archived Honest John dataset, with the official figures kept alongside, and reopened for new submissions. CarAdCheck is not affiliated with Honest John or Volkswagen Financial Services.
If you used the Honest John Real MPG section before the site closed in 2026, this is where the Mercedes-Benz sl figures now live. The owner-reported averages above were rebuilt from the archived Honest John dataset (archived page, 2026-06) alongside the official NEDC and WLTP figures and new submissions from CarAdCheck readers, and the section is open so they keep improving. Real-world figures also feed the running-cost estimate in our free advert check.
CarAdCheck is not affiliated with Honest John or Volkswagen Financial Services. How we rebuilt Real MPG.
Fuel economy is one line on the Mercedes-Benz sl running-cost sheet. These guides cover the checks that stop you buying the wrong one.