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W140 S500 Octane Grade

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Raja Taimoor, Feb 19, 2010.

  1. Raja Taimoor

    Raja Taimoor Active Member

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    Hello!

    Recently purchased a W140, S500, 1996. The previous owner strictly advised me to stick to 95 rather than 91 octane grade fuel whereas the operator's manual recommends Premium Unleaded Gasoline: Posted Octane 91.

    Could shifting to 91 make any difference on performance, engine or the mileage. And should I consume the present tank of 95 till reserve before refueling with 91. I mean could mixing up of the two grades in the same tank be harmful to the engine in any manner.

    Note: 1. The car has 138K Km on the clock with a perfectly healthy engine.
    2. I am a very reserved driver in the town and hardly go higher than 140kmph even on the highways.
     
  2. Cole@MBS

    Cole@MBS Forum Supporter Authorised Forum Supporter

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    Stick to the higher of the 2!!!!
     
  3. shayes

    shayes Senior Member

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    shows I never look at pumps I thought the available octanes were 95 or 98ron.

    I stick in 95 as I seem to think that was what was recommended for my previous 500SEL which was made when leaded petrol was still around (I think??) 1985. Tempus fugit!
     
  4. television

    television Always remembered RIP

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    And a third :D 95 ron is the one to use safely
     
  5. matthewm1965

    matthewm1965 Senior Member

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    I always use the super unleaded in mine, as per the manual.
    Though I have used a tank full of the cheaper stuff and didn't notice any difference.
     
  6. television

    television Always remembered RIP

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    You really are wasting your money using 98 ron in your handbook it says use 95 ron the same as mine
     
  7. grober

    grober Senior Member

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    Depends what country you live in but I would definitely stick with the 95 octane as a minimum.
     
  8. shayes

    shayes Senior Member

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    Just don't touch the E10 Eco stuff in France.
     
  9. television

    television Always remembered RIP

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    Never heard of that one Stuart,,is it very low fuel
     
  10. shayes

    shayes Senior Member

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    Its being sold in France by BP and possible Esso. One BP Service station I went into somewhere between Orleans and Rouen had totally gone over to E10.

    I've cribbed this comment from a thread on the subjct on the Total France forum
    "Ethanol is about 35% less efficient than petrol, so if you use E10 expect a fuel consumption increase of about 3%."

    Specifically made for French cars is another comment.
     
  11. television

    television Always remembered RIP

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    Thank you very much Stuart,,I have not been through France in a long time
     
  12. shayes

    shayes Senior Member

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  13. matthewm1965

    matthewm1965 Senior Member

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    You are right Malcolm. I was misreading "premium" grade as "super" It does indeed say use 95 RON and only use 91 RON as an emergency.

    I know some engine management systems are self adapting and can take advantage of a higher octane fuel. Don't know if this is the case with the MB V8 500 engine though.
     
  14. television

    television Always remembered RIP

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    There will always be those who insist that these engines will run better on 98 ron,, twice I have filled up with 98 on a long run, and my return 250 mile trip was worse on the consumption side, others confirmed this too the last time it was discussed. Yes you can use 91 as a minimum,,but do not belt the car when using this,,and yes the engine can adapt so that you can use it
     
  15. ncooper

    ncooper Senior Member

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    Compatible vehicles.
    Mercedes-Benz: All models in circulation from 1 January 1993 except models
    following:
    - Equipped with a V12 engine;
    - Equipped engine 271 942 in circulation from 1 January 2002 and December 31, 2005;
    - Class A Turbo;
    - Class B Turbo;
    - C 200 CGI Sports Coupe (Type 203) equipped with motor 203 743;
    - C 200 CGI Break (Type 203) equipped with motor 203 243;
    - CLK 200 CGI (Type 209) with motor 209 343;
    - CGI CLK 200 Cabriolet (type 209) equipped with motor 209 443.

    Regards,
    Nick.
     
    Last edited: Feb 20, 2010
  16. shayes

    shayes Senior Member

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    Is that suitable? or unsuitable for these cars, Nick?

    Back to the title please
     
  17. ncooper

    ncooper Senior Member

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    Sorry,edited to make it clear.

    Regards,
    Nick
     
  18. OP
    Raja Taimoor

    Raja Taimoor Active Member

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    Thanks for the replies members!

    Does 91 have the potential to give the 'knock' on this S500. Shouldn't this car be having the system to adjust to the different grades, including 91.

    Where I live, 95 is 33% costlier than 91 - good enough reason to find the less expensive but safe alternatives for the guzzler!

    Regards
     
  19. brandwooddixon

    brandwooddixon Senior Member

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    Yes the system can self adjust BUT there are physical limits as to how far it will go.

    If you use 91 RON instead of 95 RON you'll get bad running when under load, especially when cold, although all will appear well when cruising. Pinking and knocking which will damage your engine if used for a long time.

    I made this mistake the first time I drove an unleaded petrol car in Germany. German standard unleaded is 91 RON, unlike the UK's 95 and their Super Unleaded is 95 RON. I only discovered this when we came to leave a hotel after an overnight stop. I just kept topping the tank up (every quarter tank) a couple of times to help improve the octane content.
     
  20. grober

    grober Senior Member

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    Depending on your model of car and the type of its ignition control units you may be able to remap the ignition to use the lower grade of petrol. This involves changing a reference resistor on the EZL/AKR units. see this page. http://www.k6jrf.com/MB_DI.html
    This may have already been done on your car I don't know. You would have to check the values of reference resistor plugs R16/2
     

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