knepster

I accidentally filled my C55 with 89 Octane. I usually use Mobil and blue is their ultra premium. I filled up at Exxon and blue is their midgrade. Is my engine toast?

cte430

You're not screwed. You'll probably see less perf. and worse gas mileage as your ECU makes the adjustments for the lower octane.

respdoc

Yep..time for the junkyard..

vimzin

call me the trash man ill be at your house to pick the car up tom around 9am

TECHNICIAN

it will be fine. maybe a check engine light with some misfire codes, but it will be ok

respdoc

lol..

This thread would be more interesting if this guy filled up with diesel... :p

Marktini

You will see some misfire (potentially) and the code may appear. As soon as you are down 1/4 tank fill it with premium, then again, then again... don't run the tank to empty.....

av2

Fill the rest of the tank with 91/92 and run it easy.

respdoc

It's fine to play it safe side but I would be highly surprised if he notices any change at all.

1) I used to fill up my E-class rentals all the time with 89 oct. gas for a good 2-3 weeks with no problems

2) The car, unless changed to "performance", is in a default fuel setting that accepts at a minimum a 89 octane fuel rating..


So, relax, sit back, and enjoy life...your car will be fine..

Jon Winter

Add a can of 104 black octane boost.

05C55

I fill my wife's leased 745Li with cheap gas whenever I get stuck filling it. I can't tell if there is any difference in performance and mileage seems unaffected. I use mid grade in the C55 when available as testing has shown there is ZERO benefit between 89-92 ron.

Improviz

In a normal motor this might be true, but in a high performance motor with an 11:1 compression ratio, it is not. Mercedes specifically warns against using regular unleaded in their owners' manual, stating that using other than premium grade may cause engine damage and void the warranty.

Here's what my manual has to say (I duplicated their boldface font as well):

Caution!
To maintain the engine's durability and performance, premium unleaded gasoline must be used. If premium unleaded is not available and low octane fuel is used, follow these precautions:

- have the fuel tank filled only partially with unleaded regular and fill up with premium unleaded as soon as possible,

- avoid full throttle driving and abrupt acceleration,

- do not exceed an engine speed of 3000 rpm, if the vehicle is loaded with a light load such as two persons and no luggage,

- do not exceed 2/3 of maximum accelerator pedal position, if the vehicle is fully loaded or operating in mountainous terrain.

It goes on to say:

Damage or malfunctions resulting from poor fuel quality or from blending specific fuel additives are not covered by the Mercedes-Benz Limited Warranty.

Road & Track also discussed octane ratings here:

Porsche Octane

I am the happy owner of a 1995 Porsche 993, which I recently purchased. Per the owner’s manual, recommended fuel is 93 octane, yet in the San Francisco Bay area, all I can find is 91 octane. I asked a local Porsche repair shop for advice, and to paraphrase what I was told: “The factory found out the cars can’t really burn high octane gasoline properly. Therefore, we recommend using regular gasoline (87 octane), which will keep the car running cleanly.”

At first I accepted the idea, but now I’m nervous about it. I do recognize the anti-knock sensor will help, but even then the manual says use a minimum octane of 90. I also recognize that excessive octane is useless, but shouldn’t the highest octane rating for an engine also produce the highest power? Even more important, as the 993 has plenty of power for my taste, is there potential for damage to pistons/cylinder walls, etc., using 87 octane? I’m sticking with 91 until I get your reply!
Joe McPeak
Walnut Creek, California

Answer:
We’d trust the owner’s manual more than the local expert, especially when it comes to a minimum octane rating. What Porsche is telling us via the owner’s manual is the car runs best — makes maximum power — using 93 octane fuel. In other words, octane higher than 93 is unnecessary and, as you point out, won’t do any good.

The manual also says the minimum octane is 90. While there could be any number of reasons the engineers selected this as the minimal rating, we can make a relatively safe assumption that 90 octane is the lowest anti-knock rating the knock-sensor and engine-management system can reliably accommodate by reducing ignition timing and thus also horsepower.

There may even be a slight safety margin built into the minimum octane rating to account for environmental conditions (extreme heat), but in any case 90 octane is what Porsche says is the lower limit, and, yes, power will likely be reduced when running that fuel. Clearly, 91-octane premium fuel, the highest octane commonly available in California, meets that minimum requirement.

Now, under favorable conditions — average temperatures and light-duty driving — you can likely get away with 87 octane. But if the temperature rises or you put your right foot down, 87 may not be enough to avoid pinging. This could lead to engine damage over the long haul.

Finally, considering the investment you have in a 993, why quibble over what — in this price range — is a few dollars’ worth of fuel? Assuming 15 mpg and 10,000 miles driven a year, the annual difference between $1.40/gal. regular and $1.80/gal. premium is $266.80. Given the peace of mind, better performance at full throttle and extra detergents in premium fuel, we’d reach for the 91-octane pump.

schwarzwagen

i you are concerned about gas prices, you should not be driving an mb anyway, go back to your hondas.


its an 11.0:1 compression engine, who in their right mind would use mid-grade in such a high compression engine. a mistake is ok, just drive with caution and refill asap to dilute. but, using mid-grade as a regularly accepted practice is stupid and will only damage the engine over the long run.

PsssTkiD

just drain it.

05C55

I disagree based on years of personal ownership of twenty or more high performance cars and motorcylces, Corvette, Porsche, BMW, Mercedes, every serious SS litre bike and MX bike produced in the last 6 years, that octane rating has adversely affected anything I have driven. I do use mid grade, but admittedly I have been filling at Costco and using premium but I am not stupid and my car does not knock.

If you are going to quote scripture in your sig, it would be nice if you did not openly call people stupid. I do not believe you actually have the knowledge or experience to back up the claim that prolonged use of 89 oct will damage an AMG motor.

Improviz

Do you think the engineers who designed the car have the "knowledge or experience" to back up such a claim? Because they, for some odd reason, stated exactly that in the owners' manual, as I quoted above, and I will quote it here again:

Caution!
To maintain the engine's durability and performance, premium unleaded gasoline must be used. If premium unleaded is not available and low octane fuel is used, follow these precautions:

- have the fuel tank filled only partially with unleaded regular and fill up with premium unleaded as soon as possible,

- avoid full throttle driving and abrupt acceleration,

- do not exceed an engine speed of 3000 rpm, if the vehicle is loaded with a light load such as two persons and no luggage,

- do not exceed 2/3 of maximum accelerator pedal position, if the vehicle is fully loaded or operating in mountainous terrain.

It goes on to say:

Damage or malfunctions resulting from poor fuel quality or from blending specific fuel additives are not covered by the Mercedes-Benz Limited Warranty.

It seems pretty ludicrous to argue that the manufacturer would needlessly insist upon the usage of premium unleaded, provide detailed instructions as to how to drive if low octane fuel is inadvertantly put in the car, *and* would also state that engine damage as a result of poor fuel quality is not covered by the warranty, if using low octane fuel were in fact harmless.

As the tech page at Road & Track stated, when it comes to octane rating, I'd trust the owner's manual.

farooq

we use octane 114 here in saudi as a standard.. how abt that...

RenaultFreak

you'll be fine, you won't notice the difference unless you know your car very well.

05C55

If this were true, there would be a half dozen high performance cars with detonated internals strewn about my lawn. I don't believe for a minute there is any profit motivation behind such a recommendation, like putting Mobil 1 in as factory fill oil, you probably think using pennzoil mineral oil would cause the engine to fail. As I mentioned, there are reports that actually test the properties of gas, I saw it with my own eyes, I will see if I can find it, the differences between 89-91 were insignificant. My car runs great on either 91 or 89, you cannot tell the difference, the car does not pre-detonate and in my opinion is not even at an increased level of risk. Now the guy who buys this car after I am done with it.... Well that might be another story.

Improviz

....versus the opinion of an owner, I'll defer to the designers, and to the company who warrants the vehicle, and more importantly, will or will not be approving any warranty-related claims.

The fact that your engines didn't disintegrate neither proves that you did not have detonation (in fact you can have inaudible pinging in an engine), nor that they did not suffer detonation-related damage...and I don't believe that Mercedes is involved in the oil/gasoline sales or distribution business, so I doubt that any profit motivation is involved...nor do I believe that they would go to such lengths to warn against potential engine damage if there were no chance of it happening.

And you have yet to produce any documentation showing that lower-octane fuel doesn't hurt performance or raise the potential for engine damage in a high-compression motor, which is because no such data exists; it is a fact, not opinion, that high compression motors require high octane fuel, period.

Gasoline faq, including data on compression ratio and octane:

Definition of octane and its relation to compression ratio:
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The 5.5L AMG V8 is a high compression motor. Period.

Stop spreading disinformation, and get informed. You're as wrong as wrong can be on this matter.

05C55

I question if you have ever wondered about the quality of gas that goes into your car? For example, are you always getting a 91 RON at the pump? Fuel ditributors are people too and just like everything else, there are shortcomings. Manufacturers must consider these conditions when desigining a car. Yes premium is recommended for optimal performance and efficiency, but as you can see, you are unlikely to damage a modern engine with sophisticated anti knock sensors and ingition and fuel injection systems.

ctC230K

and i bet it costs like $0.05 cents a gallon too

Improviz

That is not what we are discussing. The discussion is whether or not using fuel of an octane rating below that recommended by the manufacturer will affect performance adversely and can damage the engine. Whether or not people occasionally make mistakes or are dishonest is a side issue.

The higher engine compression ratio used in these cars will make the onset of knock under high engine load a virtual certainty if regular unleaded is used, which is why Mercedes specifically warns against doing it in the owner's manual that you're arguing that people should ignore. The effect will be for the engine's ECU to dial back ignition timing, which means that the spark in the combustion chamber will not occur at the optimum time, which will affect both performance *and* economy, as is discussed in the portions of the FAQ you chose *not* to quote, even though they were more pertinant to our discussion than the one you did.

Frankly, I think what you are doing here is kind of sneaky, in that you are deliberately omitting information which would be informative to your fellow AMG owners rather than concede that your original assertions were incorrect. Case in point: you selectively quoted data from the gasoline faq . You quote question 6.13, but do NOT quote from the very next item in the faq, which is far more pertinant to what you're trying to argue:

In other words, the same source which you quoted explicitly states that NOT meeting the engine's octane requirement CAN cause engine damage, AND lowered performance, AND poor fuel economy.

This is also addressed in question 6.16, which you also did not cite:

And finally, just as I said before, the higher compression ratio (11:1) of the AMG motor DOES increase the octane rating requirement:

So, if you want to save a few pennies a gallon by using substandard fuel, fine...but you are doing your fellow AMG owners a great disservice by deliberately omitting pertinant information. As noted above, what will happen in response to using substandard fuel is predictable: the engine knock sensor will detect knock, and the ECU will retard timing to avoid it. This in turn will result in both lower economy, and lower performance. All for what? To save a few pennies on gas? But if it lowers your fuel economy by dialing back the ignition timing, what have you saved? And if it damages the engine and Mercedes refuses to warrant it, you're looking at some serious bucks to get it fixed...for ten cents a gallon?? Why gamble on such a pricey investment?

You could save a lot of pennies on cars too, by not buying Mercedes...
What's the saying, penny wise and...

CynCarvin32

got to love peopple that have 2 60k + cars who cheap out on a few bucks worth of gas.

you saved a few bucks when u bought gas. how about a cookie? all that money you saved is enough for a nice big freshly baked cookie. Yummy

11:1 compression needs 91 oct gas. Good thing you dont have a kompressor car. that thing would just LOVE low oct gas!

05C55

Got to love people with poor math skills. My savings would be about $500 a year based on my consumption. Mid grade does not seem to effect the mileage of the car at least the info from the trip computers does not suggest it is suffering. Multiply that over three years and invest the proceeds and the pot continues to grow. I don't give a flying **** about my wife's 745 and though I like my C55 quite a bit, it will be discarded in a few years as well.

The original question was, will low grade damage the motor? My answer was and is no. I believe that even with prolonged use it wil not damage the motor. You do have valid points regarding efficiency and I don't blame anyone for adhering to the owners manual, but Mercedes is not a charity, they are profit motivated and there is a plethora of CYA in everything they do.

You can put rocket fuel in as far as I'm concerned. Mid grade is fine for the wife's BMW and I won't hesitate to use it in my C55.