I don't want to start any wars or anything, I just want to ask a question to people who know, or have the owners manuel for the older cars.
I seem to remember reading somewhere that the 84 and 85 500 engines required only 87 oct fuel. I don't remember where I read it or even when.
I have always used the best fuel I could find however, at this time money is tight, and gas prices are high. Yesterday, when I went to get gas, 93 oct was $1.76 and 87 was $1.56. So I says to myself, I'll give it a try. So I did. The car runs the same, no spark knock, starts good, idles smooth, etc.
I don't have an owners manuel for this car (why to people take the manuels out of the car and not return it?) so I would like for someone who has an 84 or 85 500 SEL to look in there manuel and see what it says.

Thanks

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84 500 SEL (307,xxx miles)

I would like for someone who has an 84 or 85 500 SEL to look in there manuel and see what it says.
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I have an '86 560SEL and the manual calls for premium. I have used regular in the car and it runs fine with no knocking as the timing will adjust automatically to the octane level. But the car does run better and has more power with the "good stuff" in the tank and does get a bit better gas mileage with premium. I am sure your car was intended to use premium...best to stay with the factory specs.

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1986 560 SEL (159K miles)

You could probably find the owners manual either online or at a dealer..They can't charge you more than $20

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David Weis
Old Rides================
70 250
73 450SL
78 300D
88 Grand Am
Current Rides=============
95 280C *
98 SL500 *

PG. 11 of the Approved Service Products List, "Model years 1975-1985 and model year 1986 190 E 2.3 Use unleaded regular gasoline meeting ASTM standard D439. The octane number posted at the pump must be at least 87 min."

So any gas 87 and up can be used. Would you benefit from a higher octane, well that's another debate.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Rick - Rockman asked about a 5.6 litre V-8. You posted info about a 2.3 litre - not the same animal.

Rockman - I have a 126 car with the small motor and it calls for 91 Octane, so I suspect your big V-8 would need at least that much.

At sea level or close to it, premium is 93 octane - maybe 94 in some places.

I wouldn't dream of feeding the beast anything less than premium, whatever it's octane level is wherever you live.

Would you feed Wal-Mart Tuna Fish to Miss America?

I believe that the 5.6L V8 doesn't have adaptive knock control, so you should hear via pinging if your octane is too low.

As your engine ages and accumulates some deposits (all do), your octane requirement may creep up. My 88 BMW 735i was spec'd at 87 octane, but I found after 170k miles that it took 89 octane to keep it from pinging. The pinging was only noticeable at high RPMs and heavy throttle - and I backed off as soon as I heard it.

Higher compression engines require higher octane - so the 400E/E420 engine, with an 11:1 compression ratio would require a higher octane that an engine witha 9:1 compresison ratio. Check and see what the 5.6L ratio is - it's probably 9:1, and 87 should be OK for it. Run 89 just to be sure.

Troy
1995 E420 75k

Thanks Rick
Thats exactly what I wanted to know. Do you know where I could get a copy of the "Approved Service Products List"? That is just the kind of information I have been looking for.

Thanks again,

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84 500 SEL (307,xxx miles)

The Approved Service Products List is available from MBUSA for free. Look for their phone number on the web site. The web site is mbusa.com and the phone number is 1-800-FOR-MERCEDES (1-800-367-6372).

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95 E320 Cabriolet, 159K

1991300SL,

I read Rick's post to state that all cars model year 1975-1985 can use regular as well as a 1986 190E 2.3.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record