In summary, if you burn lower than 91 your car will sense it and use a fail safe combustion timing that will give you less power and poor fuel economy. Burning higher octane fuel will not burn any different. It will however give you more power because having a more stable combustion, your ignition is easier to predict and the ECU will adjust your performance to match. I'm not sure if Mercedes' stock programming has a timing curve for 93 octane, but if you use an aftermarket tune it will.

 

That's not entirely true, we had someone in here who had a performance tune, but lived in like the Virgin islands or something where high grade fuel wasn't available and it did in fact damage his engine. If you're using 87 grade and the stock Mercedes ECU program, than it will just run like ****, but if the fuel is in poor condition, or you've modified your tuning, than you very easily can damage your engine.

The obvious answer to all this is to simply use the fuel grade recommended by the manufacturer. Anything less is like sticking AAA batteries in something designed for AA. Even if it might work, it doesn't make any sense.

 

I only pump 94 Octane. As far as I know, here in Ottawa, the highest you can get is 94 Octane at Sunoco.

94 is usually only a few pennies more expensive than 91. That increase gets lost in the shuffle.

M.

 

i put mid-grade 89 every now and then and no problem..

 

To answer the OP, I pump RON 98 which is 95 Octane, and the sticker on my fuel door says RON 98 Super Plus, courtesy of my ECU tune.

 

SHELL V-POWER BABYY AND THATS THE ONLY GAS ILL EVER USE!

 

A bit off topic but for guys around the midwest do not use fiesta mart gas....
75% water

 

I filled up my car this morning and it made me think about this thread...

My car took about 15 gallons of premium. General price difference between regular and premium here in Illinois is $0.20 a gallon.

If I chose to fill up with regular I would have saved a whopping $3.00 - now let's say I fill up once a week - that's $150 a year in total savings for putting the WRONG octane of gas in your car.

If you are that concerned about spending an additional $150 a year on gas, you should not be driving a Mercedes Benz in the first place !

Nick

 

I guess I will jump in at this point since I am an engineer in Detroit and work in automotive.

First of all, think of higher octane gas as being more refined (kind of like filtered). It has fewer impurities in it vs. a lower octane fuel. (this is all tested on a special engine made by Dresser Waukausha Engine in WI) Gas with a higher octane is more consistant (in terms of temperature) when it burns (fires).

Most (if not all) new cars come with a "knock sensor". This sensor on the engine block, is basically a vibration accelerometer that detects "out of sequence" ignition vibrations. This is were a cylinder fires when it is not supposed to. When this sensor picks up this out of sequence vibration, it sends a signal to the engine ECU to retard timing until the vibration goes away.

The higher compression of your engine, the more likely an out of sequence may occur. This is due to very complicated Thermodynamics, but let's just say the increased pressure during combution can cause pre-mature detonation before spark is fired. This can cause structural falure to all sorts of physical compontents in your engine. This is why timing is retarded to prevent this from happening.

So, to sum up, a higher octane gas is less likely to cause these misfires vs. lower octane and the higher compression your engine, the more you should be careful with octane you should be. This is why race gas has such a high octane rating as most have high compression engines (tuned this way) or they are running super-chargers or turbos (or NO2) which increases compression.

VPDFAN

 

you are the man,thanks a lot,do you prefer cheveron gas than any other gas?

 

I think any "name-brand" gas with a high octane rating will work. I would stay away from any off-brand gas. Many times the large "name-brand" gas companies will reject a shipment for quality reasons (like not meeting proper octane requirments). This is sometimes sold to the off-brand places at a reduced amount. Many of these off-brand gas stations only have 1 or 2 locations.

 

surprised no one pointed out e-85

 

Is this a serious question ? -_-

 

Sunoco 93 is the best according to my father in law, who is a Chemical engineer for Hess refinery. His job is to test fuels and oils for Hess, and he claims that Sunoco has the best detergents and the highest quality gasoline compared to others; Texaco is second . He also says that Mobil 1 is the best oil, go figure. Also, the C class has very high compression, 11:5:1 I think, or close to it; this means you must use high octane for the slower burn rate if you want the engine to perform as it was designed to. You do have anti knock sensors, but you really do not want them to be working; what they do is retard ignition timing to derease the pinging, or gas expolding in the cylinders instead of burning because the lower octane will burn too quickly causing pre ignition which can damage the valves in the engine. If you use the proper octane, 91 or above, than you can rest assured that you will not have pre ignition and therefore no engine damage. You will also realize the full performance from your vehicle, and you will get better MPG using the higher octane, because it burns slower than the lower octane. You cant go by your cars initial MPG estimator because it will reasd off of a full tank preset memory in the PCM of the last ten times you filled up and average it out to compensate.

Use 91 octane or better. Get the full performance and MPG from your vehicle and keep the anti knock sensors from having to keep your engine from being damaged due to pre ignition. Also, the savings are miniscule; about 20 cents a gallon. I think the car has a 16 gallon tank, at that rate it would be $3.20; if you need $3.20 that badly every week you need to sell the Benz and take the bus. 89 octane is actually a mixture of 87 and 91, most stations pull from both tanks, the premium and the low grade, so it is really hard to guarantee an accurate 89 octane rating, as you are getting a mixture of both. Dont be a cheapas*, use the high octane!

 

I would agree with anyone who says to use the proper gas for the car (i.e. what is specified in the Operator's Guide and inside the gas filler door label). However, could you explain how higher octane gas burns slower? I never hear of that. Do you perhaps mean that it has a higher ignition temperature? Using higher octane gas (above the manufacturer's recommendation) will certainly not yield higher MPG if that's what you are saying.

 

In a car designed to use higher octane gas, you will get better MPG from using it than if you used a lower octane, reasons being that higher octane "burns" slower than lower octane, and at a lower octane than recommended you will retard your ignition timing, causing poor gas mileage.

There are two types of octane numbers for gasoline, the Motor Octane Number (MON) and the Research Octane Number (RON). The ASTM methods for MON and RON use the same test engine, but operate under different
conditions. MON is a measure of performance of the fuel at high speeds or under heavy loads, while RON repersents the performance during low speed conditions. The octane number displayed at the pump is the average of these two values ([R+M]/2).

Octane is a measurement of a fuel's resistance to ignition. Ideally, the air/fuel mixture will ignite at the proper time ( Usually and ideally a 14:1 air fuel ratio) and burn smoothly through the power stroke. The idea is that one powerful combustion of the air/fuel mixture is better than several randomly-ignited small flame fronts. When you can precisely control the point at which the fuel will ignite, maximum performance of the engine can be achieved, and power-robbing knock and ping will be eliminated. Knock and ping are a result of abnormal ignition, or multiple flame fronts colliding within the combustion chamber during the compression stroke.

All reputable fuel manufacturers determine the octane rating of their gasoline in the research lab using a special, dedicated single cylinder engine. Comparing the gasoline to a series of standard reference fuels in the test engine results in either a research octane number (RON) or a motor octane number (MON) depending on a set of operating conditions. The RON is determined with the test engine operating at 600 rpm, at standard barometric pressure, and the intake air temperature set at 125 degrees Fahrenheit. RON is primarily used to address part-throttle knock and ping problems. The MON addresses wide open throttle operation and is determined with the test engine spinning at 900 rpm, also at standard barometric pressure, and the intake air temperature pumped up to 300 degrees.
The best predictor of a fuel's performance in a street/strip machine is the Anti-Knock index (AKI). This is simply the average of the RON and MON numbers, or (RON + MON) / 2. Most all octane ratings posted at the pumps are determined by this AKI formula, and are the minimum values you could expect to see. The minimum octane requirement
of your engine is determined by several variables besides the compression ratio. The engine and cylinder head configuration, air/fuel mixture, timing, coolant temperature, atmospheric pressure, relative humidity, and ambient air temperature will also affect the octane required to make your mill produce maximum power.


The burn rate of a fuel is a measurement of the time required for complete combustion of the air/fuel mixture. The notion that octane ratings affect the burn rate of fuel is about 180-degrees from reality; burn rate is a function of several variables, and the two are completely independent, although there is generally a correlation between octane ratings and burn rates.

Gasoline: Mobil Super+ unleaded, 92 octane (min). Color: yellow-green. Gasoline Density: 0.75 grams/mL. Air Temp: 16 to 18 deg C. 1 gallon = 3.785 liters = 3785 mL = 2838.75 grams = 6.25 pounds.

Burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate, that reduces power and efficiency for the reasons stated above. Many modern car engines feature a knock sensor – a small piezoelectric microphone which detects knock, and then sends a signal to the engine control unit to retard the ignition timing. Retarding the ignition timing reduces the tendency to detonate, but also reduces power output AND FUEL EFFICIENCY! Because of these systems, under certain conditions of high load and high temperature, a given car may produce more power with a higher octane fuel. With a LOWER OCTANE fuel, these engines systems will be reducing power to control detonation, while with a higher octane fuel, the engine will produce full power. And some modern high performance engines are actually optimized for higher than pump premium (93 AKI in the US). The 2001 - 2007 BMW M3 with the S54 engine is one such car. Car and Driver magazine dyno tested a car and found that the power output increased as the AKI was increased up to approximately 96 AKI. Also, these systems can result in HIGHER FUEL MILEAGE MPG for cars designed for the HIGHER OCTANE fuels.

Saying the higher octane burns slower may have some truth, but it really boils down to better blending and the ability to handle higher temperatures than lower octane fuel.

Hope this answers any questions. In and of itself, high octane dosnt get you better gas mileage; but in a car designed for it, you will get better MPG than using a lower octane fuel, so you basically save no money in buying the cheaper fuel and you also hurt your performance and possibly your engine; for a $3.00 difference a week in price!?!?!?!?!

USE THE RECOMMENDED OCTANE !!!!!

 

You DO all know that all the gas companies fill their tanker trucks from the same refineries, and that the only difference between one brand and another is the additive package... Right? Ok. With that out of the way...

Chevron's "Techron" additive and Texaco's "System 3" additive are basically the same thing: They're detergent packages that help to keep deposits from forming on the backs of your intake valves and in your fuel-injectors, etc.
However... There's not enough detergent in EITHER brand (or any of the others) to keep your valves PERFECTLY clean, so if you care about that sort of thing, you should periodically run a bottle of valve/injector cleaner through your fuel system.
Any Chevron station will sell you a bottle of Techron; it's pretty cheap and is recommended (by name) by Porsche, BMW, and maybe a couple other manufacturers.
Personally, I prefer Redline SI-1 or SI-2 (same stuff, different bottle sizes). It costs just about the same, but may be harder to find.
The recommended dosage for prophylactic purposes is one bottle every few thousand miles. For curative purposes -- like if your car's running poorly and you suspect clogged injectors -- the dosage is two bottles in a tankful of gas followed by one bottle in each of the next two tankfuls.
Be aware, if you've never poured a bottle of Techron or SI-1 into your tank before, that it may loosen deposits that have formed in the system ahead of the fuel filter. Those deposits will break free and be captured by the filter, potentially clogging it and necessitating its replacement.

The only difference in an 8000 gallon load of gasoline is the 1 QUART can of additives they dump in separately!

 

BTW, My dad worked for Sun Oil (Sunoco) refinery for 40 plus years, my father in law works for Hess as a Chemical Engineer, my uncle owned a Gulf gas station, and I am in the Automotive business working for a new car dealership, with an AAS in Automotive Technology as well as being master ASE certified; I think I am qualified enough to answer questions on this thread!

 

Sell ur C300 and get a Honda Civic, then u can go all the way down to 85! BRO! It mercedes ! If you cant pay the extra few cents for the car, go with the JAP car ( Like Lexus ), my frd puts 87 on the RS300, and still works fine for him. Do you know why Lexus can take 87? Cause they use the same VVTI engine as the Toyota model, like Corolla, Camry and other SHIX ! Oh well, that just my opinion..... do w/e u want .. it ur car, if u really want! dont put 89 man ! put 87 ! if you want to be cheap ! then be the cheapest !

 

I was not advocating otherwise. btw, thanks for all the fun facts but I was only questioning whether lower octance fuel burns at a slower rate (what you said), or whether it ignites at a lower temperature and also whether using higher octance fuel than recommended by the manufacturer will result in better gas mileage (which I say is not true).

 

I agreed with all - Ultra (94) from Sunoco is the way to go. I have always filled with Ultra since day one I bought the car. On Sunday on my way home, I stopped by Sunoco to fill-up my tank fearing that the price will go up on Monday. I fill with ONLY one notch down from the FULL level with 91; think me saving a few cents. I was WRONG; I drove the same hill every day, but after added 91 in the mix with 95. I fell the car was Not accelerate at all even I floored the gas pedal. It's like the car is tell me - "YOU DUMB *** - Why 91 - I'm chocking on this and I Can't Breathe" - No more 91 for me. If you love your car then go with 94 Ultra. You'll get Love if you Put Love in.

 

Yes, I do know that the only difference between the gas chains are the additive packages... That is what I said in my post. Which is why I have recommended every couple thousand miles to switch the brand of gasoline. I have read many reports and talked with people familiar to the subject. After a while (thousands of miles on the same gas), the additives themselves start to build up, so it would be best to switch the gas brand to get some different additives in to take care of buildup that not only that particular additive can't remove, but also to help remove buildup of the first additive.

While Porsche does reccomend fuel additives like Techron, Mercedes Doesn't. Soemthing to do about having an adverse effect elsewhere along the chain and drying out some lines. But I'm no expert...

 

You got to be kidding with that comment lol, im sorry i cant take u seriously after saying that. it doesnt make any sense at all. why wouldnt your car accelerate when you fill your C300 with 91 and make you FLOOR the Pedal Such nonsense. This is not a Ferrari, it should work with 91, 93 and so on as long as its not 87 or 85.

 

What I meant is that it felt like the ignition, fuel system recalibrating it self or some sort. It doesn't accelerate like normal when you floor it.

 

It's a mercedes, go for 91.. Non-californians are lucky with their 91+ octane! That stuff is hard to find in socal!