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My first three tanks were in the +26mpg range. My last was 22mpg. The only difference I can think of is the lower mpg was with 91 octane without ethanol. I normally run 93 octane with 10% ethanol. We will see what the next tank reads.
My first three tanks were in the +26mpg range. My last was 22mpg. The only difference I can think of is the lower mpg was with 91 octane without ethanol. I normally run 93 octane with 10% ethanol. We will see what the next tank reads.
While the higher octane makes sense, ethanol contains less energy per volume than gasoline so typically worsens mileage.
Last edited by GregW / Oregon; 06-09-2019 at 10:44 AM.
Curious if anyone is using regular octane instead of premium. I know it says to use premium but I was told regular is safe to use, too. Just may not get full power and at a cost of some fuel efficiency. For the latter, I think the math may make the savings in fuel cost outweigh the savings in fuel economy. At least, in theory. Has anyone actually tried this? Asking about the 350.
Curious if anyone is using regular octane instead of premium. I know it says to use premium but I was told regular is safe to use, too. Just may not get full power and at a cost of some fuel efficiency. For the latter, I think the math may make the savings in fuel cost outweigh the savings in fuel economy. At least, in theory. Has anyone actually tried this? Asking about the 350.
That's a really poor idea to do on a regular basis. You lose performance, fuel economy and over time a dirtier engine internally with out the advanced additives in top tier premium and likely increase tailpipe emissions. This is not some econobox. This is what the manual says (note the warnings):
Last edited by GregW / Oregon; 06-10-2019 at 04:38 PM.
Completely agree with GregW. You'll end up with engine knock and reduced performance if you use 87 octane regularly. It'll ultimately cost you more money. There is a reason car companies recommend certain octanes.
It was the dealer that said this so I thought it wasn't a totally insane thing. And I've seen on the Internet (which, I know, is full of expert opinions ) where it said modern engines aren't as susceptible to the problems that made this a bigger concern in the past. Anyway, I was curious what people are actually doing. Thanks for the insights.
It was the dealer that said this so I thought it wasn't a totally insane thing. And I've seen on the Internet (which, I know, is full of expert opinions ) where it said modern engines aren't as susceptible to the problems that made this a bigger concern in the past. Anyway, I was curious what people are actually doing. Thanks for the insights.
If it was someone in the sales department that told you this I would take it with a degree of skepticism. While it is true modern engines will adjust timing and other parameters to avoid or reduce knock, in doing so you are hurting the efficiency of the engine and even likely damage it over time. Rather than take the internet experts' opinions (myself included) I would rely on the rather strong language in the manual excerpt I posted. The engineers sweat the details to make the best powertrain possible; to compromise that out the door seems like not the best idea.
Last edited by GregW / Oregon; 06-10-2019 at 12:32 PM.
You won’t damage your engine. You will lose power and possibly some fuel efficiency. This issue is probably worse in modern forced induction engines at high compression. It may not be worth the cost savings. In California, the price of 91 premium is only 20 cents a gallon more than 87. In many other states the price difference is much greater. The computer will detect the knocks and adjust accordingly, and this is definitely true if you are always putting 87 in your car rather than one errant tank of gas. Modern cars are smart. If you’ve ever had a spark plug go out and had a cylinder deactivated by your computer, that episode probably causes more stress to your engine than years of running 87 gas. It is more harmful to switch back and forth from 91 to 87 to 91 to 87 than to constantly run 87 (where the ECU has already adjusted and is not constantly readjusting back and forth as knocks are detected from octane swings back and forth). Running 87 gas probably also affects emissions. It’s crazy what manufacturers will do to get government credits for emission or efficiency. Like BMW factory filling 5w-20 engine oil in their high performance B58 engine instead of a much more protective 5w-30 or 5w-40 which also meets BMW long life approval.
My father in law only uses 87 in his E350 and it has been problem free for the 8 years of ownership. However, it has a non turbo engine.
I like how the words "IF YOU WANT MAXIMUM ENGINE OUTPUT" are in bold before the only use 91 octane recommendation.
Also noticed how the DAMAGE DUE TO WRONG FUEL specifies unleaded low-sulfur fuel with low alcohol percentage and does not mention octane rating as a cause of damage.
In my country we have only 91 & 95. So I can use either of them???
Usually mercedes here emphasize on using 95 only.
Use 95. There are three main octane rating systems worldwide. AKI, used in the US & Canada, runs 4-6 points lower than most of the rest of the world. This explains it:
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.
Anti-Knock Index (AKI) or (R+M)/2
In most countries in Europe (also in Australia, Pakistan and New Zealand) the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).
Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity, and is not typically published for those countries that use the Anti-Knock Index labeling system.
Last edited by GregW / Oregon; 06-11-2019 at 10:00 AM.
Use 95. There are three main octane rating systems worldwide. AKI, used in the US & Canada, runs 4-6 points lower than most of the rest of the world. This explains it:
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.
Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.
Anti-Knock Index (AKI) or (R+M)/2
In most countries in Europe (also in Australia, Pakistan and New Zealand) the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).
Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity, and is not typically published for those countries that use the Anti-Knock Index labeling system.
Thanks, but I'm no Harry Potter. But I have over 50 years experience with cars and enjoy German cars & researching things (aided by my training and experience as an architect). Current GLE project is adapting my W166 20x9 wheels to the V167 for Winter tires. All the lug holes will need to be bored out (already have drill bits ordered), rears will need 12mm spacers (in contact with a company for that) and extended lug bolts for the rears (found US-made titanium but pricey). All this is made harder because of the newness of this car and these changes. A challenge! Luckily, I have 4 months or so to finish this project!
Attached is a pic of the wheels I am adapting from my '12, refinished in Lamborghini grey with silver added by a local company. I think they will be very passable for Winters. As I reported in another thread, they are actually heavier than the thirteen-spoke 21x10 RWA's with same width tire (the titanium bolts would help.
Last edited by GregW / Oregon; 06-11-2019 at 09:51 PM.
Here are my GLE450 numbers: 14.7 l/100km or once converted, 16mpg. Not so good, but I only travelled 199km (120 miles) since getting the car last Friday. I hope it gets better because the diesel 350 I had before was less thirsty by 40%.
Just back from a 720-mile round trip from Portland to far Eastern Oregon in my GLE 450. On way over ran freeway in Eco mode, 80-90 mph much of the time. Last 60 miles was in Sport+ on very windy, hilly road running hard. Got 21.5 mpg. This is from the return trip, which was similar.
Curious if anyone is using regular octane instead of premium. I know it says to use premium but I was told regular is safe to use, too. Just may not get full power and at a cost of some fuel efficiency. For the latter, I think the math may make the savings in fuel cost outweigh the savings in fuel economy. At least, in theory. Has anyone actually tried this? Asking about the 350.
Think of 87 as McD's and 91 as healthy eating.
Eating McD's once in a while isn't going to kill you or cause any long-lasting damage to your body.
But eating it all the time will lead to obesity and other negative health effects. It's not something you'll notice right away, but over time it will have it's negative impact.
For the price you're paying for the car, a few bucks per tank is a drop in the bucket.
05-30-2019, 07:31 PM
And I've seen on the Internet (which, I know, is full of expert opinions 
