CLARIFICATION

With gas prices hitting $5.29/gal in some places of Florida, (ABC News) I think it's important to let you all know the latest in my octane investigation. Lately there were several threads on this topic, (Octane Fuel Requirements for our GLK) where several members asked if it was okay to use mid grade fuels in the GLK. Some members (myself included) indicated that the Operators Manual was in conflict with the sticker on the car. (See above)

The sticker clearly indicates the use of 95 RON/recommended and 91 RON/min (or 91-87 Pump Octane USA).... or does it? I originally called DOT/NHTSA, Mercedes, and various shop foreman who thought as I did, that when in doubt, default to the sticker on the car at the time it was made. In fact it was discussed that the sticker was not in error but written in the European RON standard and that a new sticker would clear up the confusion in favor of the USA R+M/2 Pump Octane rating.

However, after lengthy discussions again today, it's the "lack of proper wording" on the sticker that's now thought to be the culprit... supporting the argument that the OpMan is correct and the sticker was wrong all along. They're now saying the sticker should HAVE read: 95-RON min (91 R+M/2 min). If this is true, then it would mandate the use of nothing less than 91 Pump Octane USA in our cars, something the sticker currently does not say.

Well the OpMan may be correct after all. So to those that I disputed that fact with, my apologies! (... and please don't ask for your $50k check either... thanks!) The sticker is rarely wrong if ever and that's what I was going by! But the jury is still out... an answer was promised by next week.




Please note: (AKI or AntiKnock Index, Pump Octane Rating, and R+M/2 are all the same measurement for the USA.) Confusing I know!

 

This is why I like reading your posts -- besides being very knowledgeable, you are honest as well.

 

Wow, thanks for the heads up and thanks for all the great info you post on this forum.

 

Firstly, if you were to follow "your own" rule, for a change, set forth in sticky Message to ALL Noobies, should this thread rather be a post on thread Premium Gas in my new GLK.

Secondly, as ohlord referred to, from the GLK Operator's Manual - 2010: Only use premium unleaded gasoline. Difficult to understand?

Thirdly, it seems you now are in line with opinion expressed about the subject more than half year ago: https://mbworld.org/forums/glk-class...89-octane.html, post #25. Speech is silver - listening is gold.


:
BTW: Have you noted, that in the last five disputes on this forum, are there six combatants, five individual signatures - and one in common; guess who?

Errae humanum est, ignoscere divinium -.

 

 

Thanks!

 

Great info. Thanks for doing the research. I'm always impressed when people admit they may be wrong and try to clear it up.

 

good post

 

Thanks!

Well I heard back from Mercedes Benz/USA this morning. They agreed that the sticker is indeed "confusing and misleading". (Actually it's in error!) She said that it has been forwarded to a product review to determine if a sticker change is required. Considering that the sticker currently does not reflect the octane rating system here in the USA and that there may be a fuel crisis on the horizon if the middle east does fall deeper into chaos, I hope they do make an attempt to clear this up.

Here's an example of a corrected octane rating sticker that was sent to them:



Here's the original again for comparison:

 

It is confusing especially when all vehicles have to be able to use 87 octane (US) via EPA/DOT mandate in case 91 octane is not available; even if the manufacturer mentions only use enough to get 91 octane back in the car, i.e. short term usage.

Anyway, thanks for your hard work in trying to get this confusing mess corrected.

Frankly, I think it's a mistake for the German manufacturers to mandate premium fuel except in their high performance vehicles. Engines in the 'regular' performance vehicles could easily be tuned to run fine on 87 octane (US), and then also be able to use the extra octane in 91 (US) should the owner wish to use it. The 87 octane would be cheaper for the owner also.

Regardless, our GLK has only been fed a diet of 91 octane (US) since new and that's what we'll continue to use unless 91 octane isn't available when we're about empty.

Bish

 

^ same here 91 only, didn't buy 45k car to save money at the pump.

BP can have my extra 5 dollars per tank.

 

FYI for Canadian Owners

I sent this thread to MB Canada and this is the reply I received.

@font-face { font-family: "Cambria"; }@font-face { }p.MsoNormal, li.MsoNormal, div.MsoNormal { margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: "Times New Roman"; }div.Section1 { page: Section1; } "Thank you for your email.

While we can appreciate that the label may be confusing to some consumers it should not be seen as a significant risk.

The label specifies that the vehicle is to run on gasoline with a RON of 95. It also notes minimum octane of 91 and although it does not specify that this 91 value is in reference to the Canadian/US octane rating system of averaging R and M values, it is unlikely to lead to mis-fuelling for the following reasons.

Should there be consumers who are not intimately knowledgeable with octane rating methodologies, they will see a minimum of 91 and will understand that this is consistent with what most fuel providers rate their premium fuels at in Canada. "

 

That's a rather large assumption for them to make!

 

$5 per tank?

Here in SoCal, where gas is never cheap, it's usually ten cents from 87 to 89 and another ten cents from 89 to 91, a 20 cents/gal upcharge max.

Just how much gas does your GLK hold..?

 

It's all moot... 91(R+M/2) or better... pay up or don't drive.

 

The more I read the simpler question I'd like to ask: My first tank was regular gas filled by this cheap salesman. However, I never heard any engine knocking. Does it mean it's OK to use regular (87) if no engine knocking? I don't care the maximum power, etc.

Will never fill anything below 91, otherwise it means I am not ready for such a nice car.

 

It's not ok to use regular (87). The knock sensor should prevent knock / engine damage, but you will still likely do damage to the catalytic converters. Further, you will most probably notice a loss of MPG as the engine runs less efficiently. For this reason, running regular truly saves you very nearly no money at all.

 

Thanks for reminding me the "catalytic converter" part which I forgot.

 

Geeeeeeeeeeeze. All you had to do was ask Mrs. Wayne. Since June, 1999, the only fuel permitted in our 2 Volvos and now HER Mercedes-Benz is premium. Period. End of story. There is no conflict.
She also knows to follow the tire pressure numbers on the fuel filler door.
When in doubt, check with the Spousal Unit!

Wayne

 

What is "Premium"? 91 or 93 even 95? Around me, the highest is 91 so I have to call it "Premium".

I heard in certain area the highest octane is not 91 but lower.

 

In Texas, Premium is 93. Between Texas & Boone, NC, Premium is generally 91. We just buy the highest available number. So far, that has worked well for 3 vehicles and something approaching 285,000 miles. That's all I know.

Wayne

 

That really sizes it up, folks. Buy the highest octane available. It's 91 out here in California. On our trip to Tucson and back, it was 91 all the way.

On a cross-country trip, I guess one could carry an octane booster (in a bottle) if you were worried that you might need gas in areas that might only pump something less than 91. Never seen it, but you never know, I guess.

3.5L

 

I would stay away from octane boosters. Higher octane does not translate into more HP. In fact over boosting your Octane can really harm your engine by delaying or even preventing proper ignition. It's really common that these boosters in a bottle can cause all kinds of other problems. Google it.

PS: They're meant for super high compression ratio engines... 12.5:1 - 14.5:1 etc etc. But at these ratios, most are fuelers anyways.

 

I only suggested adding an octane booster if a driver found themselves in a situation where they could not get 91 and were worried that operating their engine on something less might harm their engine. I fail to see the problem of boosting 85 or 87 octane to 91 for an engine that requires 91.

Not sure why you inserted the comments about HP. I made no assertion that higher octane fuel adds HP. I do understand that it's an old myth that running your 87 octane engine on 91 (or higher) will add HP. Probably won't harm anything (other than your wallet), but won't add HP.

I do understand detonation. If an engine requires 91 octane, but is operated on 87 or 85, you risk detonation, which can very damaging, even to the point of catastrophic engine failure. I've seen pistons that have been hammered by detonation. It isn't pretty.

Anyway, in this case, the idea is to maintain the factory required octane of 91 and avoid the possibility of detonation. HP will be what it will be. 268 if we're lucky.

3.5L

 

Yup, sorry... I didn't mean to put you on the spot. I thought I would just give a general warning to those out there that may not understand the concept. That said, I personally would rather run 89 R+M/2 if I had to (which is closer to 91RON anyways) than taking chances with an octane booster. Our ratings are generally lower than Europe's because ours is an average of two different rating methods... Ron+Mon/2