Premium Gasoline and Octane Question
 

Greetings,

Mercedes newbie here, and I did not start reading the owners manual* until after I gassed up the car with 87. I do not know what fuel the previous owners used, but from what I am reading, it is in my best interesting putting in premium fuel from now on.

My question is - since I have a full tank of 87, or if I find myself in a place where I cannot get premium gas, can I use a can of octane boosting product?

Thanks!
deneb

* This is the first owners manual that I have read cover-to-cover for any vehicle.

Do you notice engine knocking? You would hear it on acceleration, sometimes it’s hard to hear and I have to open a window and drive close to a building , like down an alley. Alcohol boosts octane a bit, it’s in cans of Heat that you see at stations. If your accelerating easy and hear no knocking ,I’d say just put in high octane gas after your down a few gallons. If you do hear it use an octane booster. Pre ignition isn’t good.

Engine will adjust for lower octane fuel by sensing knocking... and will adjust timing to suit... which reduces power.

Just fill up next time with Premium if you can.

It is only my second day with the car, and I have not noticed any knocking or other performance issues. I normally accelerate gently when I drive, but it did seem slightly sluggish for a 6 cylinder when getting on the Interstate. I don't know what normal should be for the CLK - it never occurred to me that it needed higher octane gas until I read it in the owners manual. I will also take a look online and see if there are some resources or tips & tricks guides for people new to Mercedes. I am sure that will save me some headaches down the road.

Thanks for the responses. I am glad that this community is here!

deneb

+

Methanol is the main component of HEET, and it does indeed boost octane, as pure methanol is ~110 Octane.

But...it will take a LOT of Methanol to get there.

Starting with a 66 liter tank of 87 Octane, you'll need to burn 11.5 liters of fuel first... and then replace it with 11.5 liters of methanol...which would be around 32 12-ounce bottles.

You're better off searching for a "true" anti-knock additive, which will contain some other molecules that inhibit fuel ignition, and be sure to drive quite conservatively. Don't fill up the tank when it's half full, it will only prolong the amount of time the engine spends with less than acceptable fuel. Use up the tank, fill it with premium, say sorry to your car, and have a look inside the gas cap - the octane requirement is even written there.

Good luck.

I will definitely say sorry to my car. It is my second day as a Mercedes owner, and I feel like a parent with a new baby and no clue. My last car was a 2006 Toyota Corolla. It has just under 300,000 miles (482,000 km) on it, and it still runs great. All that I did was pretty much fill it with gas, rotate the tires, and change the oil every 5000 miles. I just had its first clutch replaced last week - so, driving gently has never been a problem - in fact, the mechanic said she could tell how well the car was driven by the way the clutch was worn and the condition of the flywheel. I never thought much about it until she mentioned it, but like you, I feel like my cars have feelings, and I do not want to mistreat them, and want them to last.

Mercedes has been my dream car since I was a kid. I am more than willing to keep it maintained and run it according to specs - I am just clueless where to start. Good thing I stumbled over the octane requirements before I ran it on 87 much longer - I am just wondering what else I need to know. ... checking Amazon for a Mercedes for Dummies book ....

deneb

It should have a sticker inside the fuel door saying to use 91 octane minimum. Accidentally filling it once with 87 isn't going to hurt it because as stated before the knock sensors will detect knocking and adjust the timing to reduce performance. Also consider that when you filled it there was probably a few gallons of premium still in there so that will adjust the average octane in the tank up a bit.

I would advise to run it for a few days until you get to a half tank then fill up with premium. Around here premium is 93 octane so half and half with 87 would put it at 90 or so which is close enough. Then just remember to use premium at the next fill up.

I can't remember ever finding a station that didn't have premium so I don't think you need to worry about that.

Thanks. I didn't notice it the first time that I filled up, but once people are the forum pointed it out, I saw it (as they say here in the south ... if it were a snake it would have bit me).

I would like to find 93 Octane for at least this next fill up. Resources on the web are not very good for decisively locating 93 octane - at least in my area. The Find93 site lists 2 stations in Dothan, AL (where I will be when it is time to fill up), but they are just points on a map and, besides the name, don't offer much detail - plus I am sure there are way more locations than that. I appreciate the site, but it needs a community to embrace and grow it (maybe with a forum). I am debating with myself if I want to build something like it, but give it a wider appeal - like with performance fuels, customer reviews, and a community, etc. It's been years since I managed a phpBB with Drupal site on Linux. I fear that I may be like the old sports star who watches a modern game and thinks he still compete. Sorry for the geek babble ... just trying to figure out how to fill a need.

deneb

A site like www.gasbuddy.com ?

Thanks! This is cool, but it seems centered around prices. I was looking for a site that has octane listings. Either way, I don't want to reinvent the wheel if there is something already out there.

The town in Florida where I work does have 93 octane right around the corner at the Tom Thumb. So, maybe it's more common than I know. I really am a newbie to all of this.

Anywhere there is gas sold, there is 93 octane

We have some stations around here that are 91 octane.

87 is fine to use up, but fill with 91-93, whatever is available. 93 is not everywhere.

I didn’t realize it but I’ve been using 91 octane Costco for years, I get no knock and it’s better gas than other stations I’ve used.

Where does Costco sell 91 octane? All the Costco's I've been to (Chicago, Milwaukee, Madison, Indianapolis, Springfield, MA, etc.) do sell 93 octane "Top Tier" gasoline.

Even so, with 91 you will be fine.

These modern cars will care for themselves. If fed fuel below their standard, they will automatically adjust their ignition timing to keep the engine safe. You may or may not notice degradation of performance.

Some years ago, on a Lexus board, someone did a test with an LS430 V8 on both regular and premium fuel to see if he could save money by using regular gas. The car ran well enough (he wasn't pushing it, noticed no loss of performance) but he was surprised by the result. Gas mileage dropped so that the cost per mile was actually higher using the cheap regular gas!

So - accidents happen and we sometimes use the wrong grade of fuel. Highly unlikely that any damage of any sort will occur with these engines. I might not say the same if it was supercharged or turbocharged, though.

I gassed up with 93 at Sam's Club ($2.74 gal). My vehicle is considerably more responsive when I step on the gas. It was much more sluggish before, especially on hills.

Turns out 93 is pretty common. It's just something that I never needed to notice before.

91 is 95 Ron
93 is 98 Ron.

Both are a okay for our cars

As long as it is at least 95 Ron.

even plus 89 r+m/2 is fine in a pinch.

The octane ratings you see on pumps vary by the above sea level altitude of the particular location.

Here at 5000 ft asl, premium is most usually only 91. Those here seeing 93 probably live at alower altitude.

Octane requirement varies by altitude.

Not necessarily true.

I can go to Sunoco here and get 87 89 91 or 93.

Next door i cant get 87 89 93.

Depends really on the chain and what they want to offer

Mom used to live near Durango, CO, in some places 89 was consider premium.