Jmarazzo

I have a 2020 glc 300 with the 4 cylinder turbo and was wondering if anyone had any experience using regular fuel versus premium fuel. I had a 2016 Acura RDX prior and I used regular gas with no problem.

Xbowguy

Being from Pa. I alternate 89 and 92 at my local Sheetz.... I've seen zero difference in performance in the two.. Now the guy in the white lab coat at my dealer is screaming NIEN ! NIEN!

Mr. J

Consequences would be: reduced engine power, reduced gas mileage, potential for detonation at full boost under high loads.

In most locations premium fuel is only 10% more than regular. I don't understand why you would go cheap on this since it directly affects performance and reliability.

linus69

You can absolutely void your engine warranty running regular gas in this engine, being a skeptic I did a lot of research on the subject and spoke to more than one "engine-guy" about it and this MB engine definitely needs 91 octane, I use 93 in mine and it runs great.

LILBENZ230

I am not disputing the need for premium in the M274 or any modern Mercedes, but please tell me where premium is only 10% more than regular? I have not seen this in at least a decade here in GA. Right now the Chevron down the street from me is $2.19 for regular and $2.95 for premium. This is a 35% difference and top tier stations all around me are about that. Ingles Express is not top tier and their pricing is currently $2.14 for regular and $2.64 for premium, a 23% increase. This applies to every station I have stopped at for as long as I can reasonably remember.

It do remember a time when it was about 10c per grade upcharge, but those days are over - at least in the Southeast US.

pmark

i just tanked up at Costco yesterday. regular was 2.19, premium was 2.49. Only around 13.7% difference.

jimbobboy

I am under the impression that the primary reason to burn "premium" grade gas from a "top tier" company (e.g., Shell, Mobil) is that it has a "premium" detergent package that keeps the MB hi-tech engine happy without having to add an additive regularly. Its easier for me to just go to the 93 pump, but on long interstate trips cruising for hours I have burned 91 octane without noticing any loss of performance When I am back in DC with trips almost all short runs, I go back to 93.

aweber1nj

This is seriously interesting to me...

I used to put only premium (91-93 octane) in, but at one point I was casually chatting with my MB dealer and he said something like, "It doesn't actually matter that much anymore. We fill the tanks with regular unleaded here at the dealership."

So for years I've been putting regular (89) in my GLs and GLEs. Now those were 8cyl and 6cyl engines, of course. I have never had any issues with noticeable engine performance degradation or anything like that. And it's my understanding that the MPG tests between regular and premium turned out no differences (that COULD have been in an engine that was designed for regular-89 and not the other-way-around).

Now that I have the GLC, you have me thinking that maybe I should go back to premium for the smaller engine...

fabbrisd1

Well.. for reference, I don't know what "regular" is anymore since it varies widely by state... Premium is Premium .. I call Regular in my world "mid-tier".

Yes - MB fuel management systems will adjust for Premium and Mid-Tier - and with lower Octane Mid-Tier give you lower fuel economy - but that lower fuel economy will vary from state-to-state based on that state's definition for mid-tier.

In my opinion - the use of Ethanol gets thrown into the mix - Euro is max 5% ethanol - here in the US 10% and even 15% are not uncommon.

For all my MB's - every 5K miles I dose the tank with Stabil Marine Formula (Blue bottle) to clean up the ethanol in the fuel system... works great for me..

aweber1nj

I forgot about the ethanol part too. I have seen up to 15% around NJ.

Boy, I need to go read-up and re-educate myself!

Thanks.

rocket8189

My 2020 GLC300 has about 350 miles on it, so I'm a newbie. My experience is that a good top tier premium fuel that is 100% gasoline is the best for any engine. Now, I don't burn it in 87 octane engines, no real advantage based on the prices where I live ($.70/gal higher). Does my 87 octane car perform better after couple tanks full, yes it does--but not enough to justify its use versus cost difference. I also have a flex fuel unit and use E-85 in that auto; I have also used premium 100% gasoline in it--clearly it performs much better almost instantly when I use those fuels--its "fuel alcohol sensor" detects fuel in use and adjusts timing accordingly. Advantages of E-85--much better performance, removed water from fuel tank, burns cleaner--disadvantage, fuel mileage loss and if you burn it all the time there is a possibility of internal engine parts damage (you'd have to burn it over a very, very long time for this to happen but it will--alcohol is the ultimate solvent, thus the damage issue).

Having said all that, this fuelie guy believes the number one reason to burn a good, high detergent, top tier premium fuel is M-B warranty. They make it clear in the manual that failure to use premium fuel may lead to engine damage and M-B will void your engine warranty if they discover this problem. I can pay for lots of good premium fuel for the cost of a new engine. What was the saying--"You can pay me now or pay me later." I've also read that the 2.0 they are using in their C-class cars and others, in order to have sufficient power, were redesigned with multiple alloy internal parts that can be damages with lesser fuels. That wonderful little engine needs to be fed good food.

Thanks for listening.

arrow mallow

definitely use premium. You are getting slightly better fuel economy on premium. Engine knock is an actual thing.

I very rarely find 91 octane fuel though. It's always 93. and it's about a 25% premium.

Torsfromvegas

Please don’t be penny wise dollar foolish. If premium fuel is recommended it’s recommended for a reason. Don’t void your warranty.

Xbowguy

I'm getting 23 per gallon city miles with 89 oct.(2019GLC300 2.0 ) I've seen no negative results using it... My prior 2011 ML350 (150k miles) I rarely used 93 and it drove and behaved perfectly... but fuel prices are way down and the premium sting isn't as sever..

nsoltz

I only use Shell premium in 2018 GLC. For a while switched between Costco premium (also top tier) and Shell and consistently get better mileage with Shell. Noticed the same on a cross country drive last May. When Shell was not available, used whatever premium was available. When I was able to find Shell, car consistently delivered 2-3 more mpg.

ChinaBob

That's been my experience, too.

frandumont

Same thing for me too

Stark33

The plot thickens... Mine says 95 octane.

fabbrisd1

Well, Euro RON is not US Octane... 95 Euro RON is 91 US Octane

http://www.pencilgeek.org/2009/05/oc...nversions.html

Stark33

Thanks! You learn something new every day. 🙂

DeutscheBenz726

My E300 has the M274 engine that you have. I always use top tier 93 octane gas. When I bought it the dealer stressed several times that the M274 engine has detonation problems with lower octane fuel which would void both the MB warranty as well as the extended warranty. He also stressed they recommended spark plug changes every 30,000 miles.

MB2timer

I am using 93 octane, because I am not seeing a lot of 91 octane out there.
I am wondering if it makes any sense to mix 87 and 93 octane at about a 1:1 ratio, and end up with a 91 octane rating.

DanD.

Its all depends on for how long you are planning to keep your car.
If for a long time use 92 and above or next time you will be posting in Cracked piston discussion and asking why did this happen as I was maintaining my car as recommended.
Higher octane lover engine temp. Read or watch vids on LSPI.
Acura most likely was 6 cylinders engine and no turbo. Even modern 6 cylinders with no turbo runs on regular, Nissan, Jeep.
You have 4 cylinders turbo engine which producing almost the same HP and torture as Acura 216 V6. It needs clean high octane fuel, clean spark plugs and fresh oil.

Peszter

I've done it when fuel prices are high. Full tank of 93 then next fill-up at the half tank mark with 87 or 89. Run that tank near empty and fill with 93 again. Repeat. It's not much savings but it placates my desire to be thrifty.
These days gas is less than $4 so I just buy 93 from Costco.

sn202020

My 2017 Glc300 uses the cheapest 87 gas all the time. No piston issues yet so far at 230K km odo meter.

I change oil 5w40 every 5~7K km.
Spark plugs changed at 100K km.
Using Comfort or Eco mode.
Not driving hard, mostly under 3k rpm.