Does it matter if you use 87 or 93? I know mercedes says use 91 or higher but I have no idea if it matters and was told it doesnt. Anyone have any idea? I dont even know why I'm asking because its only $3.20 more per fillup for 93 as opposed to 87. Just curious

 

The person that told you it doesn't matter is wrong.

 

Octane rating is resistance to burn, if you use a lower octane fuel, you will get pre-igniton and will cause carbon to build up in the combustion chambers, on valves, and possibly damage catalitic converters.

Mercedes says to use 91 and higer because of the compression ratio of the engine, if you use a lower octane gas the fuel will ignite prematurely, robbing horsepower, causing pinging, and eventually causing the other damages I stated earlier. Whoever told you that it didnt matter doenst know what they are talking about.

 

Yes it matters. IF the car is designed for 91 octane you will depend on knock sensors to retard spark / power to prevent detonation. This is ok for a out of fuel issue on the side of the road, but if the engine isn't designed for it continuous operation could result in broken rings/blown piston. At the very least you will have to limit full throttle operation and drive at reduced power. So my reco,, if it says 91,, use 91 unless someone brings you a gallon in a can on the roadside. Jim

 

93 gives you no advantage over 91 unless the engine is tuned for it. 87 would decrease hp but I doubt you would notice it unless you race or drive at high altitude. If it really bothers you I read that MB can lower the octane requirement via software....with a corresponding drop in hp. It's my understanding that this 'option' is available because some locations in the world don't have access to anything over 87.

 

I use 93 because here nearly all the stations only offer that as high test. If I could find a name brand gas that uses 91 I would consider switching, but I don't think it would cost any less and Benzie runs fine on 93.

 

... from personal experience. In the San Francisco Bay Area, the highest octane I could readily find was 92. The manual for my '96 SL600 specifies an octane of 92 or better as the fuel requirement. So I used exclusively Chevron premium (92 octane).

After owning the car for ~1 year, it required a California smog check as part of the annual registration renewal. Although the "Check Engine" light was operating correctly (come on at engine start, then immeidately go off), it was *not* lit while the car was running. However, the engine would not pass California Smog as the ECU had a couple of registers in a 'Not Ready' state. The engine was very clean burning and easily met all emission standards. But because a couple of the ECU registers were 'Not Ready', the car not pass smog. A technicality, yes - but a requirement none the less.

After 4 months at Claridges MB (now Fletcher Jones MB) in Fremont, CA and well over $3,500 from my pocket, they could not solve the 'Not Ready' ECU register problem. In frustration, the Service Department of Fletcher Jones MB in Fremont, CA went to the California DMV to get me a one-year exemption for the smog test, so at least I could get back on the road.

At this time and purely conicidentally, I moved to Texas where they readily dispense 93 octane fuel. I had the car transported to Texas, in lieu of driving cross country. Upon arrival, my SL600 needed a tank of gas.

After filling up with Chevron 93 octane and driving around town for maybe 40 miles, I took the car in for a smog check as part of the registration transfer process. Although I told the ECU tales to the Smog Technician, the ECU registers were all in a 'Ready' state! The ECU registers have been properly set to 'Ready' ever since and the car has passed smog a second time.

Before anyone jumps on the 'Drive Cycle' routine required after MB service, I did drive the SL600 over 100 miles in California (mixture of city and freeway speeds/conditions) after all the bogus work done Fletcher Jones MB (Fremont). No, the drive cycle requirements had easily been met in CA.

Summary - Gasoline, even premium - in the SF Bay Area was border-line for my engine. I believe the engine's knock sensors (or some other sensor/s) were being activated because the 92 octane in CA was just not quite sufficient for what the engine/ECU were tuned for. Claridge's/Fletcher Jones MB never mentioned octane at all during the multi-month ordeal. By the way, the ECU and all engine components have been all factory; no modifications were performed to them. Not until the car reached Texas where 93 octane is readily available did the ECU 'Not Ready' problem go away. That is the *only* difference between the two locations. The paper-trail of dubious MB work and multiple failed CA smog inspections is a hell of a read!

No, octane does matter.

 

Use What The Owner's Manual Says To Use! They don't write those things for the fun of it!!

 

If you are going to buy a Benz, why not spend an extra dollar or two to get the gas that is recommended? You will get lower fuel economy (erasing price savings) lower power and possible long term engine damage. If $$ are so tight trade it in for a Honda...

 

One reason there are different octane ratings around the country is due to altitude. I live in CO and the highest octane at the pump is generally 91 but when I travel other parts of country I may see up to 93. My understanding is that at higher altitudes you actually require a lower octane than at lower altitudes.

Also remember that with a non-turbo engine you lose 3 to 3.5 hp per 1000 ft. of elevation gain. Another reason I stick to what MB recommends.

 

I don't recall ever seeing anything higher than 91 in this (sea level) part of the country though...

 

That is informative to hear. Have not been below 4,000 ft. for several years but recall this from some years back. I thought how nice to see 93 octane when I couldn't find it in CO. I later read what I posted. My last recollection was when I had a Taurus SHO and a Ford turbo Thunderbird and drove to NV, CA area. Maybe I should research this again.

 

In California, there's nothing higher than 91 (as Jayhawk says) except for 100 at a few stations throughout the state. It's more a matter of local refinery output than altitude.

It's true that historically mountain states had lower octane because the effective compression ratio of an engine is lower in thinner air and carburetors had no way to deal with that. But fuel injected cars, like most of ours, account for this via mass air flow and expect the same octane at any altitude. On the other hand, any unmodified car sold in the US will run on 91 octane. If you remap the ECU for a higher octane, you will have problems in some regions of the country.

 

Thanks, that explains it and brings me up to date.

 

In Austin, Texas and surrounding areas, 93 octane is the norm for premium. While I use Chevron as a rule, I have also had occasion to use Shell and Phillips 66. In fact, since moving to Texas from the SF Bay Area, I have not seen premium below 93. Could be out there - just haven't found it in this area.

 

I think you will find your losses to be greater than that, probably closer to 3.5 PERCENT per 1000 feet of elevation gain.

An imperfect estimate of loss is as follows:
1. Standard sea level pressure is approximately 30 inches of mercury (29.92 to be exact).
2. Each 1000 ft. of altitude gain is about a 1 inch loss in barometric pressure.
3. This approximation is good for altitudes up to about 12,000 ft. It is not a linear relationship, so the estimate becomes less accurate after that. At 18,000 ft. your loss is about 50%.
4. Example: at 6000 ft. elevation, your loss will be about 6 inches, out of a total of 30 inches. This would be about a 20% loss. On a naturally-aspirated engine of 200 maximum horsepower (sea-level rating), you would get about 160 max horsepower.
5. To further confuse the issue, some engine management systems are better at managing barometric pressure changes than others. An engine running too rich at altitude will have further power losses.
6. Turbocharging and supercharging throw another variable into the equation. Turbocharging is best at compensating for altitude, at the price of turbo lag. A turbocharger is free spinning, and could theoretically produce 100% power at high altitude (although there are normally some slight losses). Supercharging is a bit more complicated, since it is driven directly by the engine. The relief valve and controlling software are critical here. Losses might be estimated at one-half of a naturally-aspirated engine; but this varies.

OK, physics lesson over.

 

Thanks for the fine points - well taken. Living above 6,000 ft. much of my life it is hard to explain to people why I always want the biggest engine - only get about 75% of advertised where I live. Years ago I took my Taurus SHO and went to Death Valley and points west. Couldn't believe how easy it was to light up the tires. Try that at 8,000 ft. Can't wait for my E-550. Coming west out of Denver (5,000 to 10,000 ft) not too many people could keep up with the E-430 when a truck moved to the right for me. The 550 is considerably more potent.

 

Climbing I-70 west toward Vail is a challenge for all but the most powerful cars.

Again, turbocharging really helps here. My wife's VW Passat turbo really shines in the high altitudes. Audi, Saab, and Volvo also offer good turbo engines.

Mercedes? The E550 should be plenty powerful, but the turbo Diesels are also excellent mountain climbers.