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SL55 Spark Plugs

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by SL55 Mark, Oct 27, 2014.

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  1. SL55 Mark

    SL55 Mark Senior Member

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    Fancied having a go at changing the 16 plugs on my SL55 and saving the £300 plus I've been quoted by Mercedes. I've taken four out so far, and the threads have all been coated in this sticky goo - I assume this is to stop the corrosion I have heard about. So my question is, what is this goo ? What do Mercedes recommend using ? Will ordinary high temp MS3 castrol grease be OK ? That is what I have available. Other than that, this is an easy enough job, and highly recommended.

    [​IMG]
     
  2. television

    television Always remembered RIP

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    I cannot remember what mine were like, I did it the first time round, you do not normally put anything on the plugs, unless there was a little oil down where the plugs sit.
     
  3. WG M-B

    WG M-B Senior Member Authorised Forum Supporter

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    We use a light coating off copper grease
     
  4. OP
    SL55 Mark

    SL55 Mark Senior Member

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    Thanks Terry, that sounds like a good idea,

    Mark
     
  5. rigpig

    rigpig Senior Member

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    Was going to suggest Copper grease, amazing stuff :)
     
  6. L John

    L John Senior Member

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  7. television

    television Always remembered RIP

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    When I changed the plugs on my SL500 at 45k miles, but it was 2 years over the 6 years, they were all like new, and I did wonder myself why I did change them other than to keep the servicing intact.
     
  8. L John

    L John Senior Member

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    Indeed, the link says NGK OEM are designed for 80 to 100 thousand miles.
    I really cannot see the plugs age since installation being of any relevance.

    At £300 plus (as stated by the OP) for a dealer to do it, that's a nice little earner and not necessary at the stated intervals in my opinion.
    If they fail early there are likely other issues that need looking into.
     
    Last edited: Oct 28, 2014
  9. Philedge

    Philedge Senior Member

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    The plugs in my SL are Bosch and assumed to be the OEM ones but I don't know if they are equivalent to the Laser Iridium NGKs giving 80-100k life??

    The Iridiums have a service life of 40-50K which ties in with MB service for a change at 50K so maybe MB OEMs are the basic iridium or equivalent??

    As most people seem to report plugs in good condition when changed I guess the scheduled change is to try and ensure maintenance of stated emissions by slight overkill on servicing??

    On the grounds of reliability I changed my fuel filter at the stated interval and it was spotless so I haven't bothered with the plugs that may save a gram of CO2 if changed. The 4 plugs I pulled for a check were pristine and a clean light brown colour so can stay where they are!
     
  10. television

    television Always remembered RIP

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    A few Mechanics have said that after 6 years they can be very hard to remove, but as said in my case they were over 8 years old and came out with ease, so I fail to understand this point entirely.

    We did have the issue as well were mercedes would not stamp the service book if they did not fit the new plugs, or supply the plugs.

    Maybe we should just take one out and if it comes out easily and looks good just leave them.
     
  11. Philedge

    Philedge Senior Member

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    MB Chester stamped my service book when the plugs should have been changed but only ticked the boxes for the items that had been done. On the ESS printout they gave me it was noted that the plug change had been declined but service book all fully stamped with no mention of declining "optional" items.
     
  12. OP
    SL55 Mark

    SL55 Mark Senior Member

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    John I'll have a look in the service book later, but I think those plugs have been in about 20,000 miles and 4-5 yerars. I will confirm later. They are the MB branded NGK items. MB said they were due a change, and quoted a price which I thought was daft for an easy DIY. I have taken four out to inspect so far, and all are perfect as you see, except for the grease, which is missing in places, so I plan to wipe them off, add some copper grease, and put them back in. I will inspect them again in 18 months or so, just to check everything is still OK. I don't enjoy chucking money away and when I said I would have a go myself, the service man did not seem surprised. :cool:
     
    Last edited: Oct 28, 2014
  13. television

    television Always remembered RIP

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    Wise man,I will not fall for it again.
     
  14. Philedge

    Philedge Senior Member

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    For the stock SL500 a set of 16 x NGK PFR5G-11 on ebay currently for £82. Add in a couple of hours to change them out and £300 at MB is decidedly expensive, but the coffee, biscuits and comfy sofas have to be paid for somehow.
     
  15. L John

    L John Senior Member

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    There's a compression washer at the top of the threads which are a one time use.
    Removed plugs shouldn't be put back in, as they make not make a 100% seal.

    Yes we've all done it, myself included when messing with bikes, but on a nice car with plugs that are not easily accessible I'd always replace any removed plugs.
     
  16. OP
    SL55 Mark

    SL55 Mark Senior Member

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    That's helpful John, probably best to leave them where they are, then. :)
     
  17. L John

    L John Senior Member

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    If a spark plug stops working, unburned fuel gets into the catalytic converter and I believe it can be damaged with continued use with a cylinder misfiring.
    My guess is spark plugs are still good at the end of their service miles/time because they are scheduled for change whilst they are still well within specifications so can probably go up to twice the service miles and well over any date cut off points.

    On cars with twin spark it's less of an issue if there is a weak spark from a plug.
     
  18. OP
    SL55 Mark

    SL55 Mark Senior Member

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    Just to finish off this thread as requested, I can confirm that the plugs were last replaced on 21/10/2009, at 26,779 miles, that is 25,000 miles ago. So I think they can stay where they are for now. Thanks to all for your replies.
     
  19. Roadtoad

    Roadtoad Senior Member

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    Ive been thinking about checking my spark plugs on the CL. I believe they are bosch and have been in around two years. Ive seen some cranked spanners on ebay designed specifically for V8 engines but it looks like they are only available from America and the postage is as much as the spanner itself. Any suggestions for an alternative ?
     
  20. television

    television Always remembered RIP

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