MB Medic Mercedes-Benz Repair Guides, Service, How To DIY
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Some Mercedes-Benz gasoline cars require Premium Unleaded Gas. Use the fuel grade and minimum octane rating specified in your Mercedes-Benz owner’s manual and on the fuel-filler flap. Many Mercedes-Benz gasoline models require or recommend premium unleaded gasoline, commonly at least 91 AKI/95 RON, but the exact requirement varies by model and engine.
There is no benefit to using premium gas unless your vehicle’s manufacturer requires or recommends high octane (premium) gas.
In this guide (6 sections)
Should I use low-octane gasoline (85, 87, 89) on my Mercedes-Benz?
Premium vs. regular is not a difference in gasoline quality; one is not better or worse than the other. The difference between the gasoline grades is the octane rating. Do not rely solely on labels such as Regular, Plus, or Premium. Check the actual octane rating and compare it with the specification for your vehicle.
The octane rating measures how well the fuel resists knock, which is fuel igniting on its own under compression before the spark fires. The higher the octane rating, the higher the resistance to knock. Higher octane fuel does not contain more energy. Octane ratings are expressed differently depending on the market. In the United States, gasoline is normally labeled using AKI (Anti-Knock Index), while many other countries use RON (Research Octane Number). For example, Mercedes-Benz may specify 91 AKI / 95 RON.
Mercedes-Benz gasoline engines are designed and calibrated for the fuel grade specified by the manufacturer. Using fuel below the specified octane rating can increase the risk of knock and may cause the engine management system to adjust ignition timing and other parameters.
In some circumstances, knock or abnormal combustion can set diagnostic fault codes or show up as a misfire.
Can I use fuel system/injector treatment on my Mercedes-Benz?
Do not add fuel-system or injector-cleaning products simply because they are marketed for Mercedes-Benz vehicles. Use only additives recommended or approved for your specific vehicle and follow the product and owner’s manual instructions. We have used Chevron Techron Concentrate Plus Fuel System Cleaner on many Mercedes-Benz cars without any problems. Certain detergent additives are designed to help reduce deposits in the fuel system. Their effectiveness depends on the product, engine, and type/location of the deposits. We have used the Techron additive in Mercedes-Benz cars that have been sitting for over a year or have higher mileage and have noticed improvement after going through a couple of full fuel tanks. Always read the directions on how to use the additive properly.
Premium gas vs. regular: What is better for your Mercedes-Benz?
If you have read through forums or videos online, you may have read that you don’t need to use premium gas. That is true if your car requires regular gasoline. In that case, you will not benefit from using premium gas. When the car manufacturer recommends premium gas, then that is what you should use. Using lower grade gas for an extended period can reduce performance and fuel economy and, on some engines, increases the risk of knock. The most reliable way to determine the required fuel for your specific Mercedes-Benz is to check the label inside the fuel-filler flap and the owner’s manual.
I Accidentally Used Regular Gas Instead of Premium
If your Mercedes-Benz requires premium fuel and you accidentally fill it with regular gasoline, don’t panic. A single tank does not automatically mean the engine has been damaged. Avoid hard acceleration and high engine speeds, and refill with the recommended fuel as soon as practical. Follow the specific instructions in your owner’s manual. Just don’t make regular gas a habit: you may not notice a change in performance the first few times, but over extended periods you will.
When the Check Engine Light Comes On
If the engine starts to knock or the check engine light comes on after a tank of the wrong fuel, the engine control unit will have stored the reason: knock sensor activity, a misfire or a fuel trim fault. A Mercedes capable scanner such as the UCAN-II Pro reads those codes and shows live knock retard, so you can see whether the engine is still pulling timing after you refill with the right fuel. If the codes point at fuel delivery instead, our fuel system troubleshooting guide is the next step.
Related Resources
- Engine detonation (knocking) Wikipedia
- What kind of gasoline should I use? Mercedes-Benz Customer Support
- The Truth about Premium Gas. When to Use Higher Octane Gasoline – Kelley Blue Book.
Before you buy parts, scan every control module, not just the engine. It shows the root fault behind the warning lights and tells you whether the problem is still active. See how to do a full health check.
yes i agree 91 premium is the way to go — i have had a lot of benz — 1999 190e wit 345,000 miles and used reg gas – no problem i think because my high compression was gone–car still ran awesome–but my 1999 e320
4matic wagon 270.000 miles i used reg gas and fought my check engine light for years –finally changed to premium and check engine light has been off 3 years now–did not see that coming –so yes it matters
Thanks for information it’s really helpful:),I just stay expensive gas then.