Wha type of gas in GLC 300
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glc 300
Wha type of gas in GLC 300
I alternate between 89 and 93 and has a check engine light come on. It went away the next day and had to bring my car in for another reason. I mentioned it to them and they are claiming it’s related to putting 89 on the car which i had done for 2 years with no issues. They warned me that they will clear the code this one time but next time they have to charge me. Anyone else have this issue?
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From: SW Hew Hampshire
76 240D RIP, 79 240D RIP, 14 ML350BT-GONE, 22 GLB250-GONE, 24 GLC300, 26 GLC300 (on order)
404CPE, I totally agree, thinking back I thought my GLB250 Owner's Manual stated something similar. The use of a lower octane level could hurt the overall performance of the engine. I’ve been told through PCA that 4 cylinder turbos need a high-octane fuel, not less than (91) with proven detergent additives. They recommended I should look for these stations: (1) Shell - V Power, (2) Mobile-Synergy, (3) Chevron – Techron and (4) BP – Ultimate Invigorate. I use V Power since I have a station within 4 miles of my home.
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From: Scottsdale, Arizona
2001 E55AMG
Mid tier at least, but as always, follow the OEM manufacturer instructions.
Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777
Trenton O. Gibson
tgibson@highline-autos.com
Highline Autos
Direct: 602.909.9216
Office: 480.348.0777
Out Of Control!!
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From: San Francisco Bay Area
2019 C63CS
Inside of your fuel door there should be a sticker clearly stating that 91 is the minimum. In addition, there should be a paragraph in your owner's manual stating something to the extent that you can fill with 89 in a pinch if 91 isn't available, but if you do so you should avoid high engine loads and fill it back up with a full tank of at least 91 as soon as possible. These engines do have knock sensors and can retard the ignition to deal with lower octane fuel temporarily, but it's not meant to be the normal operating mode. Just because it's been working without a check engine light for two years, doesn't mean it's fine. That just means it took the engine two years to build up the kind of deposits that eventually cause failure. Mercedes etc. also recommend TOP TIER fuel brands, because they have the required cleaning additives to keep direct injection engines happy. Last thing you want is a clogged high pressure injector from the bad fuel that starts leaking and filling the cylinder with fuel. If that happens you'll hydrolock the engine and when that happens, you are looking at a new engine. If the car is still under warranty, they'll likely not cover the new engine as it will be obvious you didn't use proper fuel. Not to mention that they most likely noted it in your file now. If saving a couple of dollars per tank makes a difference to you, then this is probably not the right car and all those savings will be wiped out when you need to repair/replace the engine. BTW, when running lower octane, the ECU usually has to compensate with running rich, meaning injecting more fuel than is technically required in order to avoid knock. That means your mpg will be lower and you won't actually save anything in the end.
https://www.toptiergas.com/
https://www.toptiergas.com/
Last edited by superswiss; Mar 17, 2026 at 02:36 PM.
Member
Joined: May 2016
Posts: 104
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From: SW Hew Hampshire
76 240D RIP, 79 240D RIP, 14 ML350BT-GONE, 22 GLB250-GONE, 24 GLC300, 26 GLC300 (on order)
If the car is still under warranty, they'll likely not cover the new engine as it will be obvious you didn't use proper fuel. Not to mention that they most likely noted it in your file now.
https://www.toptiergas.com/
https://www.toptiergas.com/
Senior Member
Joined: Jun 2022
Posts: 374
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From: SFV
2025 C300
I alternate between 89 and 93 and has a check engine light come on. It went away the next day and had to bring my car in for another reason. I mentioned it to them and they are claiming it’s related to putting 89 on the car which i had done for 2 years with no issues. They warned me that they will clear the code this one time but next time they have to charge me. Anyone else have this issue?
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MBWorld God!
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There is a forum member here that swears by using 87 octane in their W213 E 450 with the M276 no issues in their particular use case, so ymmv but I too recommend top tier rated 91, for me I use 91 shell v-power.
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Yes, the car "will learn" how to mangage. This would be the same process as swapping from "Race Fuel", E85 or higher octane and "boat gas" (no ethenol). The car does try to learn to work with what it has in it. For me, for my cars? Well, most perforance I can get - thank you.
Oh, in the times I have had to run "Regular", in general after a hurricane when there are shortages...only once I got a CEL that worked itself out after the next start up. The other times, I got terrible milage on cheap fuel.
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Yes, the car "will learn" how to mangage. This would be the same process as swapping from "Race Fuel", E85 or higher octane and "boat gas" (no ethenol). The car does try to learn to work with what it has in it. For me, for my cars? Well, most perforance I can get - thank you.
Oh, in the times I have had to run "Regular", in general after a hurricane when there are shortages...only once I got a CEL that worked itself out after the next start up. The other times, I got terrible milage on cheap fuel.
Oh, in the times I have had to run "Regular", in general after a hurricane when there are shortages...only once I got a CEL that worked itself out after the next start up. The other times, I got terrible milage on cheap fuel.
I also like ethanol free gas, shell used to be ethanol free not anymore though. https://www.pure-gas.org/
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From: San Francisco Bay Area
2019 C63CS
In theory, low octane can work. Pre-ignition becomes an issue at higher engine loads when the turbos spool up and the pressure in the combustion chamber goes up and the heat rises, but if the car is driven mostly at low rpm out of boost, then 87 can work, but if that's how you drive the car, then just get a car with a lot less power and a much smaller engine that happily runs on 87.
MBWorld God!
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In theory, low octane can work. Pre-ignition becomes an issue at higher engine loads when the turbos spool up and the pressure in the combustion chamber goes up and the heat rises, but if the car is driven mostly at low rpm out of boost, then 87 can work, but if that's how you drive the car, then just get a car with a lot less power and a much smaller engine that happily runs on 87.
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From: Fleriduh
W212 E63S Wagon - GSL580 - E63 - E350 - C300
Out Of Control!!
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From: San Francisco Bay Area
2019 C63CS
That's from back in the days with carbureted and/or naturally aspirated engines. It goes back to the same thing. It's all about pressure. At higher altitude, the pressure is lower, so the need for higher octane fuel is reduced. However, modern turbo charged engines compensate for that, so this no longer applies. But naturally aspirated engine loses up to 20% of its power in Denver vs sea level. That reduction in oxygen and pressure reduces the need for high octane fuel with a naturally aspirated engine.
However, one point that hasn't been mentioned is that the premium grade fuels don't just have higher octane, but they often also have higher levels of cleaning additives and additional cleaning additives that the lower grade fuels may not have. As I said above, with these high compression, direct injected engines where the injectors work under very high pressure, you want to keep them clean and working properly.
However, one point that hasn't been mentioned is that the premium grade fuels don't just have higher octane, but they often also have higher levels of cleaning additives and additional cleaning additives that the lower grade fuels may not have. As I said above, with these high compression, direct injected engines where the injectors work under very high pressure, you want to keep them clean and working properly.
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From: San Francisco Bay Area
2019 C63CS
Should also mention that higher octane doesn't automatically mean better fuel. Higher octane fuel is harder to combust, so there are two sides to this. Use the proper fuel for the engine at hand. If it calls for low octane, then use low octane, and if it calls for high octane, use high octane. Each engine is designed for a certain octane level.
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2019 C63CS
Yes, regular and mid-grade are still generally lower at higher altitude for the older cars. For comparison, the standard grades here in CA at sea level are 87, 89 and 91. Pretty much can't find anything higher than 91. It's also helpful to understand how the octane rating in the USA is determined. We use a different system than most of the rest of the world does. There are two octane ratings that fuel has. MON and RON. Most of the world only uses RON, which is why if you travel to Europe, premium is 98 or higher. RON is always greater than MON. RON is the octane rating for low engine loads and temperatures. MON is lower and is the rating for high engine loads and high temperatures. MON is more important really, because it applies when pre-ignition is most likely. The octane rating in the US is the average between MON and RON. So running 85 octane in the USA means the fuel has a very low MON rating, so it's likely to detonate before it should under high loads. In the rest of the world, you don't even know what the MON rating is of the fuel, so putting in a fuel with a high RON octane rating means you should have a high enough MON rating.
Last edited by superswiss; Mar 18, 2026 at 02:14 PM.
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Junior Member
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From: SW Pennsylvania
2026 GLC300
I insist on using only Top Tier 93 octane gas.
I've been buying at Shell, Sunoco, Marathon, Exxon, and BP.
I just found out BP is not certified Top Tier so, they're off my list. Dammit, it's the closest to my house.
I've been buying at Shell, Sunoco, Marathon, Exxon, and BP.
I just found out BP is not certified Top Tier so, they're off my list. Dammit, it's the closest to my house.
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From: Colorado
G550
IThat just means it took the engine two years to build up the kind of deposits that eventually cause failure. Mercedes etc. also recommend TOP TIER fuel brands, because they have the required cleaning additives to keep direct injection engines happy. Last thing you want is a clogged high pressure injector from the bad fuel that starts leaking and filling the cylinder with fuel. If that happens you'll hydrolock the engine and when that happens, you are looking at a new engine.
https://mbworld.org/forums/w211-amg/...drolocked.html
