sts15

I was listening to CAR TALK this morning and Click and Clack swore up and down that there was no reason in the world to use anything but regular gas in any car except a car that someone drove as a high performance vehicle and cared about the very minor greater HP that you would get. They were very straight about it. They said all modern engines can adjust for ping and while you might not get the same HP, it would not hurt your engine to use the lowest octang possilbe. I love these guys and with the price of 93 near three bucks, I wonder if I used 87 for awhile if they are right? Comments?

clkal

I guess Mercedes put "PREMIUM UNLEADED FUEL ONLY" on their cars just for the hell of it =)

Tommy_s4

you have to remember benz's in germany run on 97-103, so putting 87 is just crazy.

Quadcammer

they are rated differently (ron) (mon) and (r+m/2)

sts15

But if they put 97-103 in Germany and the best we can do in the US is 93, why would 87 make any more difference? Clearly we do not have the 97 and the cars are still running. Why waste the money?

ProV1

ok so you'd rather listen to some dudes on the radio talking out of their a$$es rather than the MB Engineers who actually designed & built the cars who specifically state in the manual "Premium Unleaded Gas Only"?

no offense but if you wanna save a few pennies on cheap gas you're driving a wrong car. go drive a toyota prius.

lexrex

Premium is cheap these days, relatively speaking. It's still only 20-30¢ more than regular.

At $1 a gallon for regular and $1.30 for premium, premium is 30% more.

At $3 a gallon for regular and $3.30 for premium, premium is only 10% more.

The higher gas prices go, the more negligible the difference between the two.

OldNate

Honestly, you can put normal 87 octane fuel in the mercedes, not much will happen. Our neighbor has a E class with 182k miles and he has been using regular since 40k miles. Although, you shouldn't do this, because i'm sure it does decrease the mileage of the engine in the long run. I run premium 91 octane at all times.

MarcusF

The reason European fuel has a higher octane rating is you use a different formula. Here in the US we use the following formula:

(RON + MON) / 2

In most places around the world (including Europe and Australia), the Research Octane Number (RON) is what’s posted on the pump. There is a second rating called the Motor Octane Number. Both numbers are determined using a variable compression engine, but the MON uses heated fuel, the engine is run at a higher RPM, and the ignition timing is adjusted during the test. The MON is always eight to ten points lower than the RON. This means the exact same 98 octane gallon of UK fuel, is rated at 93 or 94 octane in the U.S.

Modern engines have knock sensors. When the ECU determines the engine is knocking, it retards the timing. The ECU doesn't retard it a little, it retards the timing to "this engine can't possibly knock now" levels. Engines with retarded timing produce lower fuel economy numbers than engines with the factory recommended timing specs. This leads me to believe that the money saved by using lower octane fuel will be negated by the poorer gas mileage. Aside from that, the cost of a single blown head gasket is all it takes to reach the point of never breaking even. All that's being discussed is "saving" a lousy $3 per tank using substandard fuel (15 gallons at a 20 cents per gallon savings). Nothing at my dealer costs $3.

Lastly, here's what they have to say on the exact same subject at their website:


Dear Tom and Ray:

For umpteen years, I have had a choice of 87 octane, 90 octane, and 92 octane gas. I always purchased 87 octane because it was the least expensive. And my cars have always performed well on 87 octane. I now have a car that has a sign on the dash that says "Premium Unleaded Fuel Only." Why does the manufacturer tell me to use 92 octane, and how important is it that I pay attention to this?

Ray: I can tell you're a cheapskate, Norma. They put a big sign right in front of your face on the dashboard so you can't possibly miss it, and instead of spending a few extra bucks a week, you stall, hem and haw, and write to us to ask if you really have to do it.
Tom: Ahh. A woman after me own heart!
Ray: And because you're--shall we say--frugal, you're going to be really bent if you ruin the engine on your new car and have to pay for a new one, aren't you? In which case it's very important that you follow the manufacturer's instructions for octane ratings--whatever they are.
Tom: Here's why. The lower the octane, the lower the temperature at which the gasoline explodes in the cylinders. And in certain "high compression" engines like yours, 87 octane gasoline explodes too early. Those early explosions are known as "pinging" and they eventually cause engine damage.
Ray: Premium gas (probably 91 or 92 octane, whatever is specified in your owner's manual) explodes when it's supposed to in your engine, and that's why the manufacturer of your car requires it.
Tom: In general, you should always follow the manufacturer's recommendation when it comes to octane. Using a lower octane can harm the engine over time, and using a higher than called- for octane is a complete waste of money.
Ray: And I guess that's the good news we can give you, Norma. You don't have to waste your money springing for 94 octane. You can stick with the nice, cheap, 92 octane stuff.

Musikmann

I like these guys too and it's too bad they seem to be expressing two differing opinions, one on their recent radio ralk show and another on their website.

I choose to believe the information MarcusF just posted, and I believe like most of the others, that you should use at least 91 (R+M/2) octane fuel in your Mercedes.

straightSIX

Why can't people decide for themselves? Why do they always seek 'expert opinion', usually from some person not even qualified to do so. Many people ask to be fooled, if that even makes sense. Information is out there. Obviously everybody has differing opinion, and stubborn people will always ignore scientific data, not to mention all the hearsay going around. So, try it for yourself and make your decision? If you dont notice any degradation in performance/gas efficiency, go with lower octane. Your engine wont blow up on a tankful of lower octane.

mannnu81

i used to listen to car talk, tom and ray are hilarious. both of them have engineering degrees from MIT, s they prob know what theyre talking abt

Hirnbeiss

When's the last time a friggin' yankee really knew what he was talking about, especially when his favorite car was a Subaru? That being said, and acknowledging that one has a Ch E degree and the other a General Science degree, they are not far off that the knock sensors will reduce detonation and probably avoid damage to your engine. However, those of us raised in the days where timing lights were staples of the toolbox know that advancing the timing results in better performance. You run regular in your Ford Windstar or Toyonda Cookiecutter. If you're after PS (Pferdestaerke) then go for the best!
I will run mid-grade through my Hengst from time to time, however, and haven't noticed any detectable change in performance or mileage.

Ramblin' Wreck '84 BSME

Quadcammer

rotfl, another genius from down south. Remind me why all the ivy league schools, and the best engineering/mathematical schools are in the northeast?

Maybe you can also remind me why the northeast houses the best finance, law, and architecture concerns?

When was the last time a hillbilly knew anything at all, besides how best to sleep with their cousin?

sts15

From all the advice, I think I will stick with 91 but dip to 89 every once in a while. There does not seem to be a difinitive answe. Just becasue MB tells you to use primium does not seem to be good enough. Why would they put the sensors and knock adjustments in, if using primium was mandatory. On the other hand, I do not want to say 3 buck a fillup just to lose a head gasket, that made the most sense to me.

On the other hand I think Tom and Ray are right most of the time and they sure are funny.

Where is PIne Brook? I live in Princeton.

Hirnbeiss

Sorry, Oliver, I forgot to let you know that I also have an Ivy League degree, so I know the schools are overrated - more like playgrounds for Daddy's rich kids (ala "W"). So you've proven my point.
Your last line also shows that you, like nearly all Jerseyites, are living in a fantasy world about what the South is like today - that's not a bad thing if it keeps you in Jersey.

Huachipato

Follow MB recommended minimum Octane. It is there for a reason.

For what it's worth, I was suprised to learn that not all modern cars have knock sensors.

lkchris

Here's the word from Mercedes:

https://www.mbwholesaleparts.com/Sta...June06Star.pdf

TruE320Ridah14

91 oct all day on both my cars, both manufacturer's say I have to use Premium Unleaded Fuel Only. 1994 Acura Integra GSR, 1998 Mercedes E320.