Lower Octane = Smoother Idle?

[EricSilver]

I have an '89 260e which I always filled with 92 or better premium fuel. I have always had a problem with intermittent shuddering at idle.

For about the past month I have been using 89 octane and find that the problem does not seem to occur nearly as much -- practically not at all now. (Sometimes, I panic and think the engine has stopped because I cannot feel or hear it running.)

I read somewhere about a year ago, either here on in the Mercedes newsgroup, that mid-grade fuel was recommended for the 260/300 but I never used it until recently.

Is it safe to continue doing this?

Eric Silver

[jeffsr]

Watch the plugs for abnormal conditions. If it isn't pinging, or spark knocking, then you're probably OK. I think MBZ recommended Premium unleaded b/c cause this country had such crappy regular unleaded.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

[JCE]

Jeffsr:

I too have an 87300E. When I first got the car I mistakenly put in a full tank of regular on the way home - the car ran fine with no pinging or anything. Since then I have been running premium as per the book, but can't help wondering if mid grade or regular wouldn't do as well. Any opinions?

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JCE
87 300E, 65k miles
Smoke Silver

I also have an '88 300E. About a year ago I tried running mid-grade and stuck with it. It seems to work just fine. My idle may be a little better since then. It very well could have to do with additive differences causing a cleaner fuel system.

Have a great day,

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Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[jeffsr]

Hey guess what?? I'm using Texaco Power Plus 89 in my '89 300E and it runs great. So go figure.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

[Aaron]

I'm sure the single cam sixes will run fine on mid-grade, but for the 104 twin cam six, I'd stick with premuim. I run Sunoco Ultra 94 in my 300E and in return I get excellent fuel economy and smooth running. You definitely can't run anything lower than premium in a V8, and from what I was told when I worked at the dealer, Mercedes recommends premuim to keep the cats and everything clean and in top condition. I tried running mid-grade in my DeLorean but found it to run horrible. It seems to like Sunoco 94 like the rest. Just my $0.02.


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Rgds,
Aaron Greenberg
MB technician
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'77 450SL
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8
'74 Jensen Interceptor Mk.III
'81 DeLorean DMC12
'85 BMW 745i Turbo

[EricSilver]

I'm happy I am not alone with this.

At the time I posted the message, I decided to add one quarter tank of 87 octane to my existing one quarter tank of 89 to see if there would be any further difference. So far there is none, but I will certainly stick with all-89 since I am most comfortable with it.

My plugs are very clean, but I do leak some oil through the back of the head gasket, but I'd rather leak oil than burn it.

Now if I could just stumble across an equally simple solution to my awful brake dust problem... (repainting my wheels for the second time this year).

Eric Silver