Does Mid Grade Gas effect performance? - Mercedes-Benz Forum

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post #1 of 17 (permalink) Old 01-26-2012, 03:43 PM Thread Starter
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Does Mid Grade Gas effect performance?

I just purchased a 1989 260e. The owner before me said he would put mid grade gasoline in the vehicle. The owner (an older man) stated that he would just take the car on short trips and not out that often. The car is 24 years old and has 89,000 miles. I put mid grade in and feel a hesitation/lag when first starting the car and driving for the first 5-10 minutes, then once the car is warm it drives fine. Would premium gas make the vehicle run better with more pep?
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post #2 of 17 (permalink) Old 01-27-2012, 09:28 AM
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Is there any octane requirement listed in the owner's manual or on the filler cap? I would try the higher octane gas to see if it helps. Or better yet, that's a W124 so find that forum in the sedans section and do a search for "octane" or "fuel".

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post #3 of 17 (permalink) Old 01-27-2012, 10:39 AM
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Lower grade gas should not have affect on starting the car. The difference will show under heavy load, when the engine start pinging.
Don't do it. If the car is design for Premium -put Premium in it. You want to run car on cheaper grade -buy a Prius.
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post #4 of 17 (permalink) Old 01-27-2012, 01:56 PM
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I have found that middle octane gas, 89, gives me better mileage than premium and equal performance in my 1991 300E.
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post #5 of 17 (permalink) Old 01-27-2012, 06:10 PM
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Originally Posted by 300E91 View Post
I have found that middle octane gas, 89, gives me better mileage than premium and equal performance in my 1991 300E.
Unfortunately that is not technically possible.
With lower octane the engine performs less, what might end in fuel savings, but those things that give you more HP and better gas mileage at the same time don't really exist.

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post #6 of 17 (permalink) Old 01-27-2012, 06:15 PM
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To the OP's issue, a quarter-of a-century-old car with only 89K miles might do well to have a little run at high rpm with a double dose of seafoam or techron.

His problem might be sticky injectors.
Also agree that 91 octane is best

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post #7 of 17 (permalink) Old 01-27-2012, 06:19 PM
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I don't understand that either. But if the 260E and 300E are based on the same platform the results of 89 mid-grade might be the same for both. Personally I will run what the MB engineers say to run in my car and that is 91 octane.

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post #8 of 17 (permalink) Old 01-27-2012, 06:23 PM
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For me, anyway, I'm pretty sure those MB Engineers know more than I do!

Same deal for K&N filters, "performance" chips, etc...

Phil

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post #9 of 17 (permalink) Old 01-28-2012, 09:04 AM
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Originally Posted by Kajtek1 View Post
Unfortunately that is not technically possible.
With lower octane the engine performs less, what might end in fuel savings, but those things that give you more HP and better gas mileage at the same time don't really exist.
Gasoline Octane rating tells how much it can be compressed before it spontaneously ignites. Interestingly, a higher octane fuel has a lower energy content than a lower octane rated fuel. The lower power content of high octane fuels can be overcome with higher compression engines, which results in a higher expansion ratio and thus a higher work output. If the engine is not high compression, it will never realize the benefit of high octane gasoline. The M103 engine in my 300E has a compression ratio of 9.2:1; it is not a high compression engine. I assume that the OP's 260E is similar.

I've done comparison tests of high and mid octane gas for more than a year. I typically fill at the same station, drive largely the same routes and always logged my data in a spreadsheet. Fuel mileage and cost per mile are clearly better with mid-grade gas. This is not anecdotal evidence.

See one of my earlier postings which cites a variety of experts and sources on this subject: post4108568.
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post #10 of 17 (permalink) Old 01-28-2012, 09:33 AM
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Its been very long time since I drove car on regular, but I remember filling our Volvo with Premium for mountain driving. This way the engine would take several hills on overdrive, while on regular it would have to downshift. My action was not focused on fuel saving, but on time saving -I was getting to the destination faster and that was my priority. That was in the times when Premium cost 25% more than regular.
Than even technically regular has minimally more energy, the higher compression engines do have much better efficiency. Not having lab test we can only speculate how much one offsets the other.
Bottom line -on regular or mid you have to drive slower and that where the savings are coming from.
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