Running 87 Octane when 93 Octane is specified
 

I'm thinking about buying a 1999-2005 gas Mercedes. I think I remember reading that Mercedes specifies using 91 or 93 octane premium.

Has anyone tried to run 87 (regular) octane gas in these cars? What is the performance difference? Does it "hurt" the engine or does the computer compensate for the difference?

The computer will compensate for it, but don't get in a habit of running cheap 87 all the time. A tank now and then is ok, 2-3 tanks in a row is not. But, at 15 cents a gallon premium it's only like $3 more filling up a bone dry tank... Is it worth it?

Cheap out on the fuel and expect to pay for it in the long run.

save $3 or spend thousands on a new engine

The owners manual will address this question. Generally it is OK if you don't accellerate hard and you keep your RPMS under 3 or 4K. Everyone likes to believe all kinds of great things about premium gas. The only difference is it resists knock more. But the truth is these threads are worse than oil threads. Read the manual. All cars are not the same. If you like to rabbit stomp all around then run premium.

You can always retard the spark to run on regular (87 octane) if the computer doesn't, but you sacrifice performance. As long as there is absolutely no pinging/knocking, you won't damage the engine; knocking is extremely damaging. If you later have a valve job, chances are the head(s) will be resurfaced, which will increase the compression slightly (unless each cylinder chamber-top is honed to compensate) and thus requiring further spark retarding. In the end, it's a trade-off between higher($) gas or lower performance.

There is no evidence the "computer compensates" and it in fact is NOT designed to do so. This is simply wishful thinking and borders on fantasy to believe so. (I'd like, BTW, to see the "timing retarded" on one of the new distributorless cars--which describes all 1999-2005.)

The typical 6-cyl Mercedes engine is around 180 cu in and develops the same horsepower as an American iron boat anchor engine of around 350 cu in. It takes high compression--and consequently premium fuel--to accomplish this. The V8s are in a similar state of tune.

Maybe it's SOP to ignore what American car manufacturers recommend, but you do so very much at your peril with German stuff.

????

What do you mean?

The computer will sense the knock and retard your spark, so you won't hurt anything. You will lose some power, and mileage.


But its false economy, and really if you are looking to buy a Mercedes and the extra $3 a tank matters...

Thats what knock sensors are for.

How do YOU think you can do it?

No it's not. They are for minor problems perhaps caused by carbon in cylinder, not for gross changes. This is "legend" that has been built up over the years, mostly again by wishful thinkers. The Mercedes manual would approve regular fuels if your fantasy were correct.

https://www.mbwholesaleparts.com/StarTuned/pdfs/LiquidJune06Star.pdf

Um well thats how ignition systems work.:confused: Thats why modern cars don't ping anymore...

PW: This was an interesting question with a load of OPENIONS. Here is some facts, help yourself, OK. I have three vehicles, all say use 93. A Volvo S-90, a 96 S-320, a 97 SL-320. I've been runing REGULAR sense NEW. VOLVO 80K, S-320 103K, and SL 78K.I use Mobile 1, 10w30 all year round. Volvo=23mpg, S=26 @ 75mph, SL=24 @ 65mph. PW, these are facts, not my openion. Have fun, the older S's are god ole sherman tanks, and the 320's get great milage for such a large car. Mine is the long wheel base model, love it. Ron

Thanks for those facts, but those are some pretty loose facts. The two MBs require 91 octane, not 93, and the Volvo claim seems suspect as well. Here's my personal experience - which I would characterize as anecdotal rather than factual - in a car that requires premium fuel the additional cost of premium fuel is justifiable in better mileage. I have always found this to be true. Try running a 6.3 on regular. You may be proud of your 24-26 highway numbers but those are not good numbers for a 104 motor on the highway. I get 29+ in an S320 on premium which easily justifies the approximately 5 percent premium price premium.

Don't forget that a premium first tier gasoline has additives that will keep the fuel delivery system clean.........

Oh really? Our minivan pings all the time when you first start it up! So does our neighbor's.....she has the same van! :D


Run premium in it if its a gas mercedes. Like has been said, if you need to save that extra $2-3 a tank then you can't afford one in the first place. :D

I don't think our 80's Benzes have knock sensors. My sisters 04 mustang pings like theres no tomorrow if you get the RPM's up.

Just a bad idea. Dont be cheap and buy premium gas. The amount you will be paying in repairs will be alot more in repairs and premium gas will be cheap once you get the repair bill.

You wont save any money on the lower octane fuel. The gallon may be cheaper, but you'll use more of them to develop the same power that the car would have made with the high octane fuel. It might actually cost you money, depending on how you drive.

bottom line - why chance it - iffen you can't afford an extra $3 per week - you can't afford the car. there are plenty of nice cars out there that will run just fine on reg. (hondas, toyos, buick, chevy). why did you buy this car? i bought mine cause of the way it handles and runs (126 lwb, v8). if i wanted to save money i would have purchased a much smaller car.

my M117 powered 450SL-C gets a little bi+chy if I run her on 87. She'll live with 89 just as well as 93 though. This is just my observation over the course of ownership.

Thats strange, it sounds more like a timing issue. It takes heat and a good load to the the gas to go bang before it should. More so in a lower compression engine like that.

That is most likely a lubrication issue. Why would it ping in a no-load situation?

You're better off staying with the higher octane. I learned my lesson by periodically using 87 and it killed the Knock sensor. After I had it replaced for $200, I realized that the cost savings from going down to 87 octane still did not pay for the knock sensor replacement.

Knock sensor is a high tech mic attached to the engine block and the moment it senses ping, it retards the timing. If high octance is specified then using regular fuel will lead to knock. OTOH if a engine specified for regular fuel knocks or knocks with high octane there are other issues to be looked into from timing to excessive carbon build up.

Just filled up the 1st time since installing my new heads, advancing the timing and correcting the crankshaft/camshaft alignment. . .goddamn. . .what a difference over 89 (i can not imagine how poorly she'd run on 87). . . A few more miles to break in the head and an oil change to 20/50 from my 10/30 flush Im running and its track time!

Instead of 20W/50 try a HDEO like Delo 400 15W-40 and you will see even better results. Engines raced with Delo 400 hardly show any wear after tear downs. There are several threads on BITOG discussing this.

hmm thanks for the tip gurkha, I'll give that a shot instead, I still need to go get oil. . .brand spankin new heads. . .a world of difference they made. . .3 way cut and all new valve guides/seals. I reused my valves and springs as they were ok, but thoes new heads gave the sluggish US spec m117 (with emissions) a real wake-up. . .

Also since you intend to race, do consider a full synthetic ATF for your tranny and synthetic gear oil like 75W-140 for your diffs. Mobil-I work fantastic to my knowledge and also Chevron Delo gear oil works even better for MB trannies. Don't worry about the wear of soft metals, Chevron Delo gear oils are EP etching sulphur free and use far better boron instead which protects the tranny well under severe racing conditions.

Just to pile on on the mileage vs octane question: My Saab, per the manual, will run on regular with less power but premium is recommended. Tracking the car shows that premium produces over 10% better mileage, usually 11-12%, and the price difference these days is more like 5-6%; it's consistently cheaper per mile to use premium. I haven't tried it in the 560 cuz that's an old enough engine I don't trust the ignition system to be that sensitive, and the manual says use only premium, but for a car of the vintage of the original poster I strongly suspect the Saab experience should be instructive.

i don't know where you folks are getting your numbers from but here the spread is at least 10% on the price of regular versus premium. If you are going to provide facts so others can make an informed decision please try to keep them accurate. Wild guesses and wayward opinions don't help anyone. Reading this reminds me of my neighbor who insists the nissan truck he just bought gets 33 miles to the gallon when everyone else with that model gets 18. I've run 87 octane in my c280 a few times and I haven't noticed one bit of difference in performance or gas mileage. Maybe I'm the lucky one and my car is just ambivalent, or maybe the little dance ritual I do before starting her up is the charm.

93 octane required but not available in socal
 

hi,
i have s600 2004. According to the manual, it requires 93 octane gas. I cant find it in los angeles. any advice?

Yes, the knock sensor will detect the knock and retard, but that means that the knock (and potentially the damage) has already occurred!

high octane
 

for supermike: You probably have 91 octane available. That is fine at your sea level altitude. Premium fuel varies in octane by altitude. Most deliveries of 93 octane are for higher altitude locations. In other words, 91 octane at sea level = 93 octane at say, Denver.

for all the rest of you: What is your problem? You bought a Benz and it likes premium fuel, so let the Big Dog drink. You can save a couple of dollars per fill-up and possibly pay a bigger price later.

If you cannot afford to put the proper fuel in the car, perhaps you should not be buying it..

Why would you need higher octane fuel at elevated altitude? The pressure in the cylinder is lower at higher altitudes, unless you have a supercharger to compensate. I think that you have it in reverse.

The problem with knock sensors retarding the spark is that this causes excessive heat at the exhaust valves. It is a very bad idea to detune a high-compression engine by delaying the spark. You could drop a valve.

unless you are racing
 

you can absolutely run regular fuel in these things...no doubt about it..the computer is actually set for that possibility. That's why when you may 'chip' the computer you must absolutely use premium, it insists upon premium fuel whereas the stock chip expects you to probably/possibly not. It's programmed for potential thriftiness ...... actually throwing premium in an around town car is worthless....As to potentional engine damage..none...remember, the fuel concerns contribute to car manufactures in a political type of fashion....

even more importantly
 

who knows what the hell octane really is?

Octane is a measure of a fuels resistence to combust. IE a 93 octane will be harder to ignite than an 87. The higher the compression, the more combustion resistence you get.

Thats the only difference, labling higher octane fuel as "premium" is misleading, it isn't any better or worse than the other. All gas is required to have the minimum amount of cleaners in it etc.

What it really comes down to is, run what the manual calls for. If spending a few extra cents on 91 or 93 really makes that much of a difference in your budget you have no business buying a high end car.