93 vs 89 Octane
 

Am interested in any technical / testing data that may be out there. The GLS450 states 91 octane must be used. My favorite and convenient station carries 87 / 89 / 93. So, without having to "blend" every other fill-up, I am wondering if 89 is really detrimental, or is it simply marginally impactful on power and fuel mileage. Thanks,

Why even risk it. Put 91 in and enjoy the vehicle!

I put 93 in my gls550, and in my 2011 e class. Wont be able to tell what it does until a few years down the line.

93 octane
 

From the instruction manual:
Given that 93 is at least 91, why not fill the entire tank with 93 and call it a day?

I have been using mid-grade gasoline in my GLS 450 with good results, no ping, no pop, smooth response, good milage,... for the last 6,000 miles.

On the other hand, I rarely go over 2,500 RPMs, and almost never floor the accelerator. My understanding is that if you do not cause the high cylinder pressures of the turbo-boost at peak TQ, then you can get by with the lesser gasolines. On the other hand, if you attempt to get all the performance out of the 450 engine in the GLS maybe you should stick with 91 octane.

For someone who just paid over $80K for a truck, would saving $6 - $10 per gas tank be that important? Now, if it's a lease and you don't care about the truck, then it's a different story.

I agree, whether a person can validate effects or not, the engineers that designed these trucks said we should use x octane, why not trust their knowledge?

There is also a law in this country that any vehicle sold has to be able to at least limp home on the lowest octane available (87 ?) without damaging the engine.

It is your car and you can put in it any gasoline that you want.

I listen to my car, and my engine is telling me that it is perfectly happy on mid-grade gasoline.

Wasn't aware of that law, the manual does state that you can run lower rated fuel with some precautions.

I don't know the rating, however for my GLS550 I only used the high grade fuel from Costco as I feel they have a constant churn (look at the lines) and listed as top tier (likely just marketing).

I'm by no means an engineer, nor a mechanic. I trust the engineers to design a quality car, I also trust their judgement on the recommended fuel. I feel it's a rather cheap insurance to ensure top performance and longevity of my car's engine.

Love these forums, I now know about the limp home law and I'm sure there will be other things we all learn from each other.

Pretty sure my wife's gls had 87 octane when I picked it up today. Ran.....not great, loading up and stumbling 1,500-1,750rpm in 7/8/9th gears. Put in 50L of 94 three hours into the trip, then 47L 4 hours after. No more stumbling and it will kick down and hit the higher rpm range. It didn't want to before.

Here is an image from the dash on my GLS. We started in Oklahoma City and this image was taken a few miles before we arrived in St. Louis. As anyone can see, there are lots of miles (474), a pretty descent M/Hr (64) over 7+ hours of driving, and over 28 MPG. This probably represents the asymptotic limit to GLS gas consumption ?!?

I am living in Toronto and using Shell V-power 91(Ethanol free), sometime has Petro Canada Ultra 94(May contain 10% Ethanol). I prefer Shell( Works well with my Range Rover Sport for 2 years without any issue and more power)

You cannot be serious. You are spending $80 grand on a car and you want to save a few nickels on gas??!! Seriously all luxury vehicles from Germany are built for 91+ octane. You will not damage the engine with lower octane but you will not get optimal engine performance and your savings will not be as high as you think as gas mileage will be worse. Switch stations or use the 93 octane. Seriously. Why buy the car if you don't want it to run at 100%.

A) one actually gets better milage with lower octane--lower octane gasolines have greater energy content. As long as the engine is not pinging and not suffering from detonation the engine has all the octant it needs.

B) can your GLS get the milage I am getting from mine? If not, then your argument has no merit!

C) My GLS is my truck, I don't need to get 100% of the performance it has out of it--that is what my Ferrari is for.

Sams & Costco
 

Sams & costco premium is usually less then the street price for regular. Plus get a Sams club cc and save another 5%. Between 4 cars I figure I save over a $ 1000.00 a year with a $ 50.00 membership. Makes premium less painful...

I'm not too upset by mileage on my '17 GLS550 using 93 octane gas on 1k drive from MO to PA yesterday with a very full/heavy car. Considering MB reflects MPG to be 14/18 my nearly 21 is pretty good.

Whilst I cannot provide an answer for running our NA V8 GL450 on regular; its always purred puurfectly on 93...

What I can give advice on is how it drastically affected our 2.0T VW.....
It turned into a sluggish, rough riding, high idling, non-smooth machine....
Everything turned uncouth....as if it was struggling and recuperating from an alcohol infused bender...

When I feed it 93...it changes its entire demeanor to a rev happy, purring perfectly pouncing panther.......:wootrock:

So, If the GLI which VW says is a-okay to run our 87 yet really recommends 93....
imagine how it might affect your Bi-Turbo...3.0 V6......with definitely more stresses than a NA model...


Although i'm very guilty of 87 in a loaner.lol :X

hey KOMBIFAN, hilarious share on the 87 vs 93 ... I have never heard of a VW referred to as a "pouncing panther" before ... lol

thanks, am sticking with 93 top tier on my '18 GLS

Glad you enjoyed it! lol

Nice! Have you done a hand calculation yet to see how accurate the computer is? I don't have a GLS (yet), but all other MB's I've had always show about 1 to 2 mpg too optimistic on the computer estimate. Real life calculation (# miles driven / # gallons pumped) always comes out 1 to 2 mpg lower.

Gas is pretty cheap, and you're not driving a POS beater. Put the gas recommended by MB.

Some mistakes here... lower octane gas does not have less energy than high octane. That is only true if the octane booster is ethanol, if its pure gas there is no difference. Though it is safe for the engine to use lower octane gas in a pinch, using it constantly is detrimental since that means the computer must constantly retard timing to avoid predetonation, something that the turbos do not like at all. Doing so will also provide less mpgs since the engine operates less efficiently. Again filling up with cheap gas is not a death knell if you do it in an emergency but it should be avoided as much as possible.

^^^^^^^ This ^^^^^^^^^

Thanks C4004Matic ... running exclusively Premium ... and humming along ...