Should I Use Premium Gas in My Mercedes?

You bought a Mercedes Benz because they are known for their quality, performance, and long-lasting reliability. Now, you want to make sure it holds up to your expectations and that means making sure you’re taking it in for proper maintenance and regular oil changes. Maybe you’re even paying more at the gas pump for premium fuel rather than regular gas, but is it really necessary? Our import mechanic in Raleigh is taking a closer look at whether you should use premium gas in your Mercedes or if regular is good enough. 

What’s the Difference in Regular and Premium Gasoline? 

First, let’s look at the difference between regular unleaded gas and premium. Unleaded gasoline is rated by octane - regular has an octane rating of 87, mid-grade is 89 and premium is anything above 91. 


So, what’s octane? It’s the unit of measure determining fuel performance, specifically, how much compression the gas can tolerate before spontaneously igniting. As the engine compresses the air-fuel mixture into a smaller volume, it’s ignited by the spark plug. Or, that is what should happen. If there is too much pressure it will ignite at before the spark from the spark plug. Gasoline with a lower octane, like regular, needs significantly less compression before igniting than premium gasoline with a 91-octane rating. 

How Octane Affects Your Mercedes

Now that you know what the octane does, let’s look at how it affects your vehicle. Most engines can run just fine with a lower octane gasoline because the compression ratio of your engine isn’t that high. The engine doesn’t condense the air-gas mixture with as much pressure, so the spark plug is able to ignite it on the compression stroke like it should. In fact, using a high-octane fuel in a lower-compressing engine won’t benefit performance at all.


Performance-tuned engines compress fuel at a higher rate before combustion in order to improve power and efficiency. Using a regular unleaded fuel in one of these vehicles means the fuel will pre-ignite and won’t burn efficiently. This leads to the air-fuel mixture in the cylinders detonating before the spark plug can do its job which causes a knocking sound in the engine. 


Using regular unleaded gasoline in a car that is designed for premium, high-octane gasoline will cause consistent knocking in the engine. This is more than an annoyance, if left untreated or if the driver continues to put low-octane gas in the car, this can negatively affect fuel economy, minimize power and performance, and cause major engine damage. 


How long does it take for engine knocking and using the wrong fuel to cause major damage? Unfortunately, there’s not one set answer - some cars will be okay for a few months or even years of using low-octane fuel, while others’ pistons wear out or rods crack quickly. 

Does Your Mercedes Benz Need Premium Fuel?

All Mercedes-Benz engines have high-compression ratios that demand a higher octane, so the answer to the question is yes, only use premium fuel at the gas pumps. While you may think lower octane gas will save you money, any savings will be negated by the drop in efficiency and the costs of an engine repair. 

Bring Your Mercedes-Benz to Our Import Mechanics

If your engine is making a knocking sound, bring it in to our import mechanics in Raleigh. With over 30 years of service and experience, we can diagnose the problem quickly and get you back up and running smoothly in no time with an effective engine repair for your Mercedes. To schedule service, fill out our contact form or give us a call at 919-324-3019.


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