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Old 10-14-2000, 11:27 AM
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I was just reading all the documentation that can with my newly purchased 91 300E and came across a caution regaurding fuel requirments. MB says "To maintain engine durability and preformance, only premium unleaded gasoline (91 octane or higher) is to be used" it goes on to give a list of 4 precautions to do when using regular gas... no abrupt acceleration, mix with premium, don't exceed 2000rpm with a light load, don't push the gas pedal more than 2/3 if fully loaded.
Should I heed these warnings? How will regular gas effect engine duribility/longevity. Will reg. fowl injectors/filters/fuel pump?
I've been using regular gas because it's about 8-10 cents cheaper than premium.
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Old 10-14-2000, 03:51 PM
Mike Murrell's Avatar
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Join Date: Feb 2000
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Your car has an M103 motor - 6 cyl. There have been posts here and on another MB lists that indicate mid-grade gas(89 octane) being adequate for these motors. I too have an M103 motor and have always used 93 octane premium. Personally, I wouldn't use 87 octane in one of these motors. My 2 cents.

Mike Murrell
'91 300-SEL
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Old 10-14-2000, 05:25 PM
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Join Date: Nov 1999
Location: Santa Cruz, CA USA
Posts: 117
I just posted a similar statement on this topic. I cut and pasted it below:

I don't know about the new MB's but my 1986 MB really likes high octaine. Like 92. I tried to save a
couple of bucks by using the lower priced stuff, but I really noticed a difference in the mileage I
was getting. 86 octaine gets me roughly 18.75 MPG, while the 92 gets me around 23.5 MPG.
Sometimes more. Especially if I slightly overinflate the tires a pound or two. The difference in price I
think is well made up for with an extra 75 miles per tank! (Depending of course on how I drive and
how late I'm running) Since I spend an hour and a half per day commuting almost exclusively on the
freeway, I have time to notice these things. I'm going to try for 25 MPG with the tank I have now.
I've heard people argue that the brand of Gasoline makes a difference. I haven't found that to be
true. The only thing effected by different gasoline brands is my pocket book!

10 cents cheaper still isn't cheap enough when you take into account the difference in MPG. The math works out to be cheaper with premium.

Kyle De Priest
1986 300e
1972 BMW R75/5 (Best there is)
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Old 10-14-2000, 05:47 PM
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Join Date: May 2000
Location: Chandler, Arizona, USA
Posts: 804
Hello EADG,

The sky high fuel prices lately have been giving all of us headaches. Instead of opting for lower octane fuel as a way of saving $$$, may I give you another suggestion? If you do not know already, you can check out and see a comparative listing of the price of gas offered by the gas stations in your area. The service is for Canada only, and I think it does cover Ontario. I usually check it out, especially durin' the summer when the prices were VERY high, and end up finding high octane fuel at a price comparable to regular at most stations. Hope this helps a bit with your problem.

<- WaVe & DaNCe the DiScO DuCk if you spot a '95 black pearl/black Mercedes-Benz E420!!!
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Old 10-14-2000, 06:58 PM
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OK, looks like everybody is using the premium gasoline for the gas milage, which, I must admit, never considered. I'll spend the extra couple of dollars at the pump for the higher octane.
DEPRIEST, thanks for pasting your previous post... I totally forgot about the archives, anyways, the higher MPG off setting the premium price is definatly food for though.
DuckMuck. unfortunatly Hamilton is not listed on the site I'll be e-mailing 'em asking to add Hamilton & T.O.

Cheers for now.
91 300E (pics coming soon)

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Old 10-14-2000, 07:17 PM
Senior Canadian Member
Join Date: Jul 2000
Location: British Columbia, Canada
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Nevermind MPG or fuel costs, consider engine longevity and the replacement cost of said engine.


Yen-Hsen Liem
'93 500E black pearl/black leather; 89,000km; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'93 500E bornit(blackberry)/black leather; 69,000km; european delivery; 245/45-ZR17 Michelin Pilot SX; 17x8.25 factory EvoII
'88 560SL desert taupe/dark brown leather; 89,000km; Euro headlights
'87 190E 2.3-16 black pearl/black leather; 55,000mi; Euro headlights
'70 280SL white/red; 135,000mi (original); factory alloys; Euro headlights
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Old 10-14-2000, 10:49 PM
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Mike M:
You have a M103 engine not a M103 motor.
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Old 10-14-2000, 10:56 PM
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Location: ajax, ontario, canada
Posts: 773
the issue is NOT fuel economy.

because the M103 has a high compression ratio, it requires a high octane fuel. If you use fuel with an octane rating lower than that recommended, and the engine is placed under a high load, your engine will "knock".

Knocking occurs when the fuel pre-ignites due to the effects of compression (like a diesel), and this is bad for the engine. Imagine this happening as the air-fuel mixture is being compressed, before the piston hits top-dead-center on the compression stroke, and you can imagine the stresses on that piston and those wristpins.
This can be heard as a "pinging" noise when the engine is placed under load. Hence the precautions about gentle use of the throttle if your fuel has an octane rating below that recommended.

i give my car what it wants, but i also sometimes drive it hard ...

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Old 10-15-2000, 03:26 AM
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Hey boys.. I was happy with the fuel economy argument.; but the real questions I was asking (read up) were conserning the subsitution and detrimental effects of reg gas, if any. Bah

Cheers for now
79 280E (fire-balled)
91 300E
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Old 10-15-2000, 01:43 PM
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I believe "bobbyv" hit the nail on the head. "Knocking" is a no-no, over a prolonged amount of time of; city driving, up hills, high speed, and basically anything which stresses the engine from medium to hard, can be very bad.

The result, possibly over-heating of the combustion chamber (cooling system not designed for the added heat) and a warped head. Or possibly a cracked/broken piston under extremes (acceleration, heavy stress). Anyway you cut it, if you abuse the engine, it will fail.

Hope this answers your questions.
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Old 10-15-2000, 03:43 PM
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Thanks for the answer roas. I filled up with premium this afternoon.

End of discussion.

91 300E
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Old 10-15-2000, 06:28 PM
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Location: Toronto, CANADA
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I have always had bad experience using lower grade gasoline in performance engines. My dad borrowed my car once and he filled it up for me when he was done. He put regular gas in it. The difference was immediately noticeable. Mileage and performance were down. After a quarter of a tank I syphoned the rest of teh gas out and we put it in my dad's Dodge Ram. Seems to work OK there, and he has a big v-8 in it. Filled my car back up with high-test and everything was back to normal.

I also think it will keep your engine better over time.

Jason Priest
1986 420SEL
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Old 10-15-2000, 06:49 PM
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How about a 85 500sel euro the mannual says 97 octane but the highest i can find is 93. what do you think/

Dan Younes
1985 euro 500sel 223k
1986 420sel 86k soon 2 be
1981 300sd 285k sold
1979 240d 298k sold
1983 300sd 272k sold
1989 chrysler 2.2l Turbo
Leabaron 140k
1989 Dodge Carvan Se 295k
20001 Mitsubishi Mirage
1994 S500
(hopefully someday)
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Old 10-15-2000, 07:06 PM
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Gasoline is one of the major 'operating' costs of driving for many people since it costs $0.08 -$0.10/mile

Owning a MBZ for say 15 years and 150,000 miles costs at least $30,000 in depreciation and repair for a per mile cost of $0.20--roughly twice the fuel cost. Insurance costs another $15K for another $0.10 per mile.

Trying to save 8% of $0.08/mi, at best, gets you $0.007 per mile, or maybe $100 a year tops. If that amount of money makes a significant difference to you--sell the car now, you cannot afford it. You will collapse when the cost of 'hard parts' damage comes due.

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Old 10-16-2000, 10:18 AM
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Join Date: Oct 1999
Location: Tulsa, OK USA
Posts: 139

You need to see which method your Euro Octane rating method is based on. There are/were two methods that were used in the US; Reasearch and Motor methods and each used a different scale to arrive at the octane ratings. I no longer have that information in my brain; however.

If you look at US gas pumps and the Octane rating, you will see the number as derived from the formula R+M/2 which is the average of the two methods. I do remember that one of the methods was based on 100 being the highest octane number while the other could go higher (i.e., 110 Avgas, etc).

Perhaps someone else on the list with "recallable knowledge" on this might help. I do know that I run 93 octane in my 71 250C and it does very well - no ping or knock and the plugs are not damaged. Works well even when the ambient temp is in the 105+ range.

My .02


Dan Taylor/ Tulsa, OK MBCA '71 250C/'81 300TD-T
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