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You're supposed to have 91 octane or more. Either fill up with premium all the time or if you actually have 93 octane in your area, you can do 93 full ups, 89 when it gets half full, then let it run down again, fill with 93, fill with 89 at half full. But that's kind of goofy and too much thinking is involved... I just get the premium.

Rental cars get E85 ;) jk
 

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I've been on car forums for the last 15 years and I see this question come up a lot and I shake my head every single time. Here's the math folks (approximate numbers from a local station but you get the idea):

87 Gas: $3.69
89 Gas: $3.75
91 Gas: $3.84

Assuming you drive 15,000 miles a year and get a city+hwy mpg of 30, that's 500 gallons a year. The difference between 87 and 91 Octane at that rate is $75 per year. Or $~6 a month. Or two lattes (barely) or the price of a movie ticket if you are a senior citizen. For a car that costs between $30,000 and $70,000 (the range of prices I've seen for cars on these forums), that's a drop in the bucket. Sigh.
 

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I use Kool aid on mine on every second tank full.
Sorry had to throw that in there...lol. Premium all the way 94 octane Sunoco


Sent from my iPad using Mercedes CLA Forum
 

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I've been on car forums for the last 15 years and I see this question come up a lot and I shake my head every single time. Here's the math folks (approximate numbers from a local station but you get the idea):

87 Gas: $3.69
89 Gas: $3.75
91 Gas: $3.84

Assuming you drive 15,000 miles a year and get a city+hwy mpg of 30, that's 500 gallons a year. The difference between 87 and 91 Octane at that rate is $75 per year. Or $~6 a month. Or two lattes (barely) or the price of a movie ticket if you are a senior citizen. For a car that costs between $30,000 and $70,000 (the range of prices I've seen for cars on these forums), that's a drop in the bucket. Sigh.
Except the gas prices you quote .. may be correct in your area at 15 cents/gal extra for premium, but around here it's 40 cents extra.

87 is currently $3.65
89 + 20 cents at $3.85
91 + 40 cents at $4.05

500 gallons a year * .40 extra = $200/year. At 5 years, that's a grand added to the cost of driving. -- Not exactly a drop in the bucket at that point, and I could see people wanting to making sure they are getting value for that extra cost.
 

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Except the gas prices you quote .. may be correct in your area at 15 cents/gal extra for premium, but around here it's 40 cents extra.

87 is currently $3.65
89 + 20 cents at $3.85
91 + 40 cents at $4.05

500 gallons a year * .40 extra = $200/year. At 5 years, that's a grand added to the cost of driving. -- Not exactly a drop in the bucket at that point, and I could see people wanting to making sure they are getting value for that extra cost.
Only thing is before you could save that grand in 5 years, your engine would fail :D... always use recommend gas. You can spend 50k on the car but don't want to put proper gas ??

I really don't get it when people buy $4 cappuccino but crib about gas :(...
 

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I've posted this before, but it's a good read.
Here are some of the common misconceptions:

* Higher octane equals higher quality fuel (false)
* Higher octane equals more engine power (false)
* Higher octane equals better fuel economy (false)
* Higher octane burns cleaner in my engine (false)
* Higher octane is better for the catalytic converters (false)
* My car must use higher octane fuel because it is built to do so and will be damaged if this is not followed (false)

Ok, so, the above points contradict everything you’ve heard about gasolines. In fact, all of the above points do indeed have some truth behind them (under the right circumstances), but can in no way be applied as blanket statements.

What is octane?

Octane is not a rating of how good (quality) or how powerful a fuel is. It is a rating of the rate of burn for the fuel … how fast it burns. Higher octane fuel burns at a slower more controlled rate than lower octane. The engine management system is programmed to provide optimum engine performance and economy using fuel with a specific octane rating.

You may notice that your owner’s manual, the sticker over the fuel gauge or the sticker on the gas cap states a specific octane rating, such as 87 AKI or 91 RON … or both (in this example, the 91 RON is equivalent to the 87 AKI). AKI is the octane rating used in the US. RON has been popular in Europe. AKI is the acronym for Anti Knock Index and is a calculated number that is the average of two different tested octane values (RON & MON). AKI may also be represented as R+M/2 (the average of RON & MON test values).

The explosion of the fuel/air mixture, in each cylinder of the engine, is not an instantaneous event. The burn of the mixture takes a certain amount of time. Due to this, the spark (from the spark plug) occurs at a point prior to the piston being at top-dead-center (TDC) in the cylinder. The spark must be generated in a specific time prior to the piston coming to TDC, so that the fuel/air mixture is at its maximum burn (and corresponding expansion rate) just as the piston passes TDC and is ready to be pushed down by the expanding, burning, mixture. The octane rating of the fuel is one of the determining factors in how long the mixture takes to burn and, hence, how long before TDC the spark must happen (spark timing). Change the octane ….. and you must change the spark timing. If the octane number is raised (higher octane), the burn will be slower (longer burn time) than what is programmed for the spark timing and the maximum burn and expansion will occur later than TDC and power will be lost due to wasted piston travel while waiting for the maximum burn point. If the octane number is lowered (lower octane), the burn rate is increased (shorter burn time) and since the spark timing has not changed, maximum burn is reached prior to the piston reaching TDC. In this case, the expansion of the combustion gasses is trying to push the piston down as it is mechanically being pushed up toward TDC. This is bad. This is the major source of engine knock, or ping (detonation). The engine parts are actually being beat to death and are rattling. Prolonged exposure to this will destroy the engine.


Engines and engine management systems that incorporate knock sensors are capable of manipulating, or changing, the spark timing dependent on the presence … or lack of … detonation. The sensors are piezoelectric devices that are secured to the engine (typically, directly to the engine block). The sensors detect the vibration frequencies of the detonation and send this info to the engine management computer. The computer then reduced the spark timing (makes the spark happen later, or closer to TDC) in order to eliminate the detonation. Since the system can detect even the smallest amount of detonation, as well as adjust the spark timing up or down, we can actually use fuels with different octane ratings … without damaging the engine, and possibly even be able to increase engine power and/or economy.

In using a low octane fuel, with a knock sensor engine, we save money at the pump. However, we may not be running the engine at its maximum efficiency. If the engine and the engine management system are optimized to run with a higher octane, the system will be reducing the spark timing (not all the time, but under conditions where detonation is present), which will reduce power output to some degree and may reduce the fuel economy. Using higher octane, will allow a more aggressive spark curve, which will produce more power and, potentially, better fuel economy.


If fuel economy is our main goal, we can run the low octane fuel, but we need to do some testing in order to determine what octane works best for overall fuel economy (cost of the fuel, plus how much we use). Here’s how; Run one to two full tanks of low octane fuel. Track the actual MPG (you can use the On Board Computer, but we prefer a real calculated result). Next, run a tank or two of the high octane fuel and calculate the MPG. Determine the overall fuel cost by dividing the MPG into the gallon cost of the fuel. This gives you the cost per mile. Multiply this x100 so that you can have a clearer picture of the fuel costs. You can now make an educated determination of what fuel you want to run. If performance is our goal, use the recommended octane, or higher. There is a point at which the higher octane would produce no further gains, due to the limitations of the programming in the engine management system. However, the common 91 to 93 octane that we have readily available is well within the typical engine management system capabilities.

Fuel Quality -

Fuel quality is indeed an issue to contend with. However, it is not directly related to the octane rating. Fuel quality is tied to the refining, storage and transportation of the fuel.
Refining -Certainly, some petroleum companies have higher grade refining processes and additive packages. Just Google “best gas” or other such terms and do some research for yourself. Be aware, however, that you will have to filter through all of the “Internet experts”. Within a given brand of fuel, it is not uncommon for the higher octane fuel to have a fancier additive package as well.

Storage & Transportation -The cleanliness (or lack thereof) of the refinery’s tanks as well as the distribution facility’s tanks and the transportation tanks (trucks, train, etc.), can take a great fuel and contaminate it. There are federal guidelines and regulations on fuel storage facility operation and cleaning, but these are not always followed. Additionally, long-term storage will degrade today’s ethanol laced fuels faster than the pure fuels of years ago. The best we can do in these areas is stick to reputable, high volume, stations and try not to fill-up during or immediately after the station’s tanks are being filled. This can stir up contamination in the tanks (water and other contaminants).


The only thing that the octane number gives is a representation of the burn rate of the fuel. The higher the number…. the slower the burn rate. If the engine is not built and optimized for the higher octane, it will only lose power by using it. Fuel quality has nothing, directly, to do with the octane rating. This has more to do with the specific fuel refinery and what they put in it for cleaning additives, etc. The only relationship to octane is that SOME brands will put more quality additives into the premium octane grades. However, if you stick with the major brands, even the regular octane will be high quality.

Typically, installing a performance chip, or programmer (which usually advances the ignition timing as one of the areas that improves power), requires a higher octane fuel (depending on the chip). The advanced spark is occurring earlier (before the piston reaches TDC) and the slower burning fuel is now needed.

And the octane rating has nothing to do with the function of the catalytic converters.
 

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The manual says nothing less than 91. In Europe the lowest you can buy is 95. I put 89 into my 300e once and it barely ran.

Only 91, nothing lower.


Andy

AMG's Owned: CLA45, C63, C55, C43

MERC's Owned: G320, GL450, C230 Kompressor, 300E.
 

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honestly, the engineers say that most of you are full of crap. :)

USATODAY.com - Why use premium gas when regular will do?
While the article is interesting, your conclusion is baffling, since most of the posters here echo its recommendation: use the fuel that's recommended when you can.

It confirms that there is power loss, however slight (5%), when engines tuned for premium are given regular, even though there's not much likelihood that the engine will be harmed.

The article's primary point is that people whose cars require regular but who insist on using premium are wasting their money.
 

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The CLA requires premium and premium is what it should get. One who affords a luxury vehicle with all the luxury expenses that come with it shouldn't mind spending on premium gas as it is cheaper than an engine that breaks down prematurely.
 

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A lower octane fuel can burn prematurely in the combustion chamber, and thus cause knocking which is a serious issue.
 

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Premium fuel is required for CLAs in all markets (Euro, Asia, North America, etc)?

What Octane is suggested (as "Premium" can mean different in different markets)? Most of U.S. is 87, 89, and 93 Octane fuel. There is also 85, 91, 94 in various markets.
 
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