Bryce1023

Has anyone been using regular gas rather than premium? I always buy premium however a colleague of mine is using regular in his 2020 GLB and he claims that he doesn’t notice any real difference from when he was using premium. I mentioned engine wear and reduced mpg however he felt that the car ran the same way with either grade. I understand that some people that lease rather than buy their GLB don’t really care as much about what’s best for the engine. In 3 years they just turn it in and start fresh. Perhaps that should make you feel a little apprehensive about purchasing a pre owned vehicle from a dealership, I would be.

Vladimir Livson

Each car designed for a specific gasoline grade. Most German cars and GLB included are designed for premium gasoline due to fact that they have high compression ratio engines. It is possible in some conditions, with a regular gas, you could have premature self ignition (cylinder misfire) and could cause engine damage in long term. Higher octane number of the gasoline translates to higher compression of the fuel prior to ignition/combustion, and higher power output.
That is the reason you would not put premium gas into a car that runs on regular. It will ignite based on regular gas engine design and you will be wasting your money on premium gas.
Same reason we do not put diesel into gasoline engine cars. Diesel has the lowest octane number of car fuels and self ignites at lower compression ratio.

Isawelvis

I know the S h will hit the fan, but I use mid grade. Im an old guy and never push the car. If I did a lot of spirited driving I would probably do Premium but Mid grade has worked on my Mercedes ML350 (75,000) miles albeit a non turbo and I use mid grade in my 2021 BMW X3 with 4 cylinder turbo. With all the electrical computer electronics, the car can adjust for lower grade fuel, but I don't use Regular If I had a AMG model with really high performance engine, I be more inclined to put in premium.

See Car and Driver article on "Is premium Gas Worth it. Aug 4, 2019. A good article, one statement , "Your car doesn't know the octane rating of the fuel in its tank. Instead the engine controller calculates as inferred octane with closed loop logic that continually advance the ignition timing until detects knock." Very good article and they tested 4 vehicles with various grade of fuel;

OK guys pile it on !!!!!!!!!!

Vladimir Livson

The cars certainly got a lot smarter last 10-15 years, and it is a good possibility that computer can adjust/detune engine based on oxygen and other sensors. However, if something goes wrong with an engine, even if it is not related to lower grade gas, would that "smart computer" have a record that fuel/air mixture was not burning as expected and computer had to adjust the performance of the engine, and cause possible denial of warranty repair?
Not sure if that is worth the risk, at least for cars that are still under original warranty.
My wife was complaining about filling the car with premium at first, however we found that GLB has a surprisingly good gas mileage on the highway. I find it on par if not better with our CR-V 1.5L turbo.

P.S. I read the article "Is premium Gas Worth it". The way I interpreted it, do not put higher octane gas into cars that were designed for regular gas, or you will be wasting your money, which I totally agree. Some cars in the article were flex fuel so it make sense that these cars were designed to be able to adjust performance based on fuel.

skullbox15

Hard to say, but I would use mid grade if anything other than premium. I put a mid-grade once in a "real" AMG engine and it seemed fine. I didn't do it other than the one time.

hammerniski

I agree 89 is the lowest I would dare go.

That is what my manual says for the AMG:

Odd Piggy

I used mid-grade (89 octane) in my older MBs around town but they were all naturally aspirated SFI engines. No problems. Did the same for our 2015 with DI but no turbo. Again no problems. On long highway trips I always used premium (93 octane). I’m using premium in our 2 DI turbo engines.

The specific power outputs of these engines (kW/L) are 60%-100% higher than 15 years ago.

I read the Car & Driver article and it sounds well informed and valid. But the bottom line is, even at today’s gas prices, going down to a 87 octane will save maybe $11 per tankful. How much did we spend on theses cars?

dvenneman

Higher compression engines that are designed for 91 plus should be used with 91 plus. Prolonged use of lower octane changes the firing rate and is not good for the engine. You bought a Mercedes’ knowing it needs 91 - put 91 in it.