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CLA250 Spark Plug Replacement (DIY Definitive Guide)

This is a discussion on CLA250 Spark Plug Replacement (DIY Definitive Guide) within the CLA Modifications / DIY forums, part of the Mercedes-Benz CLA Forum category; Originally Posted by jmc Re plug life ... the multispark scheme wears them out quicker than typical single spark systems. So Ir was chosen to ...

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Thread: CLA250 Spark Plug Replacement (DIY Definitive Guide)

  1. #21
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    Plug wear

    Quote Originally Posted by jmc View Post
    Re plug life ... the multispark scheme wears them out quicker than typical single spark systems. So Ir was chosen to give plugs a chance at some mileage. But even Ir wont last forever. Pretty sure the car will run on old plugs though combustion efficiency and clean burn will undoubtedly suffer ... mpg is one thing ... stressing the cat is another.
    Not sure if I look forward to this plug exercise though I do need to see the residue condition and observe the chambers anyway so might as well give it a go ...
    i do not understand how plug wear manifests, if there is no visible damage, carbon deposits and the gap is per spec.
    The only thing I see is some rust on the threads and on the body of the plugs. In that respect, my plugs look a bit worse than
    Picard-s. I will post some pics tonite.

    What else ( invisible to the naked eye) can be there?

    OK, we have : "the dealer told us so" but their motives are not necessarily aligned with ours.

    I heard so far: the multi-spark scheme presents heavier wear.
    I expect wear would be erosion. But I do not see any evidence of that.
    The IR plates appear to be still there, intact.

    Can we propose some observable or measurable symptom(s)
    that indicates the old plugs are less efficient despite of their seemingly "ok' appearance?

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    jmc
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    Usually the electrode surface edges of a virgin plug are well defined and an old plug will have rounded edges
    Electrode surface quality will degrade and fine pitting may occur
    The sparks are to initiate and perpetuate the energy plasma for maximum impact against the piston all within a very brief moment and the propagation time and shape of that plasma can be affected by electrode conditions
    Some time ago I ran some estimates and for normal casual driving over typical mileage yields ~56 million sparks over 3 years ... not even Ir can stay surface and edge perfect after that
    As for efficiency a dyno will be needed to compare old against new plugs though its not just power levels but also emissions content changes and my pullitoutofmybutt guess is -5~10% power levels and corresponding +5~10% emissions at say 50k miles
    Then there are related changes like oil degradation rates per change in unburned fuel content, the associated power line surface degradation (bores and bearing journals), etc
    Amazing what a tiny spark can effect
    Someday someone may do a couple dyno runs to demonstrate plug condition effects ...

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    jmc
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    ps - i will attempt to document electrode conditions when i yank the plugs out ... hunt for surface pitting etc

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    Thanks JMC! no need to post proof, I take your word for it.
    I did the job, I am not going to undo it. :-)

    An extra bonus, I noticed my engine air filter also needed replacement, just ordered a new one.
    Has anybody tried Ecoguard?
    https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

    One thing: the seat of the plug (under the shoulder of it if that makes sense)
    had a thin layer of crusty looking deposits. I wish I had some way to clean that up, but did not want any of
    the resulting debris to fall into the cylinders. (no way to get at it with the plugs in place)
    so i decided to leave it alone.

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    Hmm.

    I am with you on the rounding of the center electrode., that could cause a weak spark. But usually it is visible by naked eye when that happens.
    Ditto for ground electrode pitting.

    The center electrode iridium tip here is a mere 0.6mm. I can't even imagine how a tiny thing like
    that could get (visibly) rounded.

    I do not see any evidence of either rounding or pitting on the plugs I took out at 86K. The color and appearance indicates that the plugs work optimally.
    I said this before but I would expect to see some of the following symptoms if the plugs were worn:

    Misfiring
    Check Engine Light
    Hesitation
    Loss of Power
    Poor Fuel Economy

    If I do not see any of those symptoms, and cannot see any damage using a magnifying glass, I have to conclude
    it walks like a duck and it probably is a duck.

    NGK rates these plugs for 100K miles. See: https://www.ngk.com/product.aspx?zpid=41480

    I think Benz is just being overly conservative again, like they tend to be.
    BTW the plugs have an iridium tipped center electrode and a platinum wear plate on the ground electrode.

    The plugs are designed so that when torqued to the correct 17 foot pounds, the electrode faces the correct way
    ie the electrode gap is towards the incoming fuel. This means that the no-anti seize and correct torque
    must be taken seriously, else you may end up with the plug facing the wrong way.

    PS. I did find one reason why changing the plugs is beneficial: worn plugs can damage the cat converter.
    I am unsure what the nuances are here, e.g.: how substantial the wear needs to be for having any effect, but I consider this the
    most convincing argument heard so far for changing the plugs at the recommended interval.

    PS2: I did find another reason to change the spark plugs early. Ease of removal. Esp, with aluminium cylinder heads, if you wait a 100K miles
    the plug may be very difficult to remove, and you may strip the cylinder head threads, which is a major headache . I think this is the real reason.
    I maintain that an Iridium fine wire center electrode and a platinum plate ground electrode should last a 100K miles without pitting or any other
    erosion.
    Last edited by coder; 01-06-2019 at 06:19 PM.

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    Yeah when I got the new plugs I marked the gap facing and noted the relative thread lead in position (which is surprising) ... there is some variance and there will be some pretorque musical spark plugs routine to get the best compromise for all 4 plug orientations ... something most dealers nor shops have no idea about why for the M133/M270.
    A couple degrees either way should be ok since the center tip has its own (unavoidable) diffraction shadow ahead of the ground arm but too much and one might as well dump a match in there.
    Gosh I tell you these modern motors are such primadonnas ...

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    Hi. Any suggestion on spark plugs for a 250 with ecu remap? I've been told to get one step colder plugs.

    Regards.

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    Colder ??? Any operational power band justification provided? I am just curious.

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    Quote Originally Posted by jmc View Post
    Colder ??? Any operational power band justification provided? I am just curious.
    Well usually when increasing boost hence power, some tuners recommend one step colder plugs. No huge powerband to show, just a CLA 250 with an ecu remap.

    regards.

  • #30
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    Well both m270 (<250hp) and m133 (>350hp) motors use NGK heat range 8 plugs so perhaps you can keep the originals

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