I have received many requests asking if it is safe to use regular unleaded fuel in a Mercedes-Benz. The basic answer is “Yes, but…” Before I explain, please read what Mercedes-Benz publishes in the most recent Owner’s Manual:
To maintain the engine’s durability and performance, premium unleaded gasoline must be used. If premium unleaded gasoline is not available and low octane fuel is used, follow these precautions.
• Have the fuel tank only partially filled with unleaded regular gasoline and fill up with premium unleaded gasoline as soon as possible.
• Avoid full throttle driving and abrupt acceleration.
• Do not exceed an engine speed of 3,000 RPM if the vehicle is loaded with a light load such as two persons and no luggage.
• Do not exceed 2/3 of maximum accelerator pedal position if the vehicle is fully loaded or operating in mountainous terrain.
Most Mercedes-Benz gasoline engines are designed to run on premium unleaded (91 min or higher). Premium fuel generally burns at a slower, more controllable rate which allows for higher compression and, ultimately, more efficiency. However, since fuel quality varies, the smart engineers at Mercedes-Benz started using some clever technology (knock sensors) to “listen” for pre-ignition and other signs of inefficient combustion. The fuel management system then adjusts the spark and fuel to compensate – up to a point. There is a limit to how much the system can adapt, hence the above recommendations from Mercedes-Benz.
If your Mercedes-Benz is a 1994 or newer model, you have this technology.
Please switch back to premium unleaded gasoline as soon as it becomes available. Your engine appreciates the good fuel – and it does know the difference.
Hope this answers all the questions.