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  1. #1
    Petty Officer 2nd Class
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    Default Optimax spark plug change/Why?

    I may be beating a dead horse with all this discussion about spark plug difference but I'd sure like to understand why the slight discrepancies and why the change from one year to another. What does it all mean?

    NGK, after conversation with them, revised their specs and sent me this info in an email:

    (Here is the current up to date application listing for this engine:


    MERCURY2006 225 hp 6-cyl. 2-Stroke 225 OptiMax IZFR5G .031

    MERCURY2004-1996 225 hp 6-cyl. 2-Stroke 225 OptiMax PZFR5F-11 .040



    So the 96-04 models use the platinum plug with the larger gap setting (.040). Because both plugs have identical dimensions besides the gap they can be used interchangeably without a problem, just be sure they are all gapped the same. Hope this helps, thank you.)

    The Merc opti manual says this:

    Digital Inductive
    1-2-3-4-5-6
    NGK IZFR5G
    0.8 mm (0.031 in.)
    NGK PZFR5F-11
    1.1 mm (0.043 in.)

    So - why did Merc change from PZ gapped at (.040 NGK figure) (.043 Merc figure) to IZ gapped at .031 in 2005?

    And - why does NGK say plugs can be used interchangeably as long as all are gapped at .040? .040 is a good bit away from the Merc requirement of .031 for IZ.

    Your knowledgeable comments appreciated.

  2. #2
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    Default Re: Optimax spark plug change/Why?

    If it matters to you that much, you should call customer service at Mercury Marine Fon du Lac, Wi. 920-929-5000 is the switch board or your local dealer should have a service bulletin on the change.

  3. #3
    Petty Officer 2nd Class
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    Default Re: Optimax spark plug change/Why?

    Well, Laddies, it all started like this. I read somewhere that the right spark plug with the right gap was important. Since that time I have posted the same basic question several different ways and still have not had anyone weigh in on it.

    In this instance, - what does it take to make a difference? Is one plug better than another. If so, why? If not, why not? And how much variation in gap makes a difference?

    I've gotten NGK/s view (which is apparently what it is - a view) and I've gotten Merc's specs. There are discrepancies. Are those discrenpanies important - or meaningful at all?

    I just got curious and depend on you folks for enlightenment.

    Now I've gotten curious to know why no one has commented in numerous previous posts. If you are able to enlighten me, why haven't you done so? If not, why are you not interested in the subject?

    Interestingly enough, of the two merc dealers I contacted, neither had a clue nor were they interested enough to refer to any service bulletin. I guess they go to the shelf, get the specified plug, and install it. And, apparently that works or there would be all sorts of conversation about it.

    I'm going overboard with this, aren't I?

    Thanks for the suggestion and the number. I'll follow up with that and post what I find out.

  4. #4
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    Default Re: Optimax spark plug change/Why?

    Ok, I don't have any current contacts at Mercury, we all got old and are retired but L made a couple of calls and this is all I could come up with. The first is a link for service bulletins all you need to do is mark the type and year at the top of thr page. http://www.ishopmarine.com/ishop/jsp...smBcatList.jsp
    The second I think may anwser your question as it.s all I can find althougth in the bulletins there are dealer call numbers, that we can't use dealing with fouling. http://www.ishopmarine.com/ishop-cat...2002/EN_22.PDF

  5. #5
    Petty Officer 2nd Class
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    Default Re: Optimax spark plug change/Why?

    The following is the service bulletin. It is a little different than the years used by NGK but the bottom line is that the new IZ plug will work fine and is an iridium replacement for the PZ plug. It states that they can be used interchangeably (with) each other. However, it does not comment on whether or not either should be regapped to match the other - or which would be the one to regap.

    Thanks, Laddie.

    MERCURY/MARINER/JET DRIVES
    2.5 and 3.0 Liter OptiMax Outboard 115 Thru 225 HP
    S/N 0G590000 and Above
    Jet Drive
    200 DFI S/N 0E384500 and Above
    250 DFI S/N 0E407100 and Above
    Situation
    As a 2003 model year running change, OptiMax (not to include Hi-performance OptiMax
    products) has switched to a new spark plug. The new spark plug has an iridium alloy center
    electrode that is smaller in diameter and concentrates the spark in one area. The spark gap
    has also been reduced.
    The iridium spark plug will supersede and back fit the platinum spark plug. The platinum and
    iridium spark plugs can be intermixed and used in the same engine.
    The new spark plug is a running change for the 2003 model year. This bulletin is to inform
    you of its presence in advance of pending service manual updates.
    Platinum spark plug NGK PZFR5F-11, Mercury P/N 33-855672 1
    SUPERSEDES TO
    Iridium spark plug NGK IZFR5G, Mercury P/N 33-889597 001
    Spark plug gap
    Platinum PZFR5F-11 1.1 mm (.043)
    Iridium IZFR5G 0.8 mm (.031)

  6. #6
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    Default Re: Optimax spark plug change/Why?

    I just tried your second link which is, of course, a repeat of what I've just posted.

    So - new question. Why wouldn't merc address the issue of mixing plug re gapping? Seems to me that it would make a difference. Maybe now is the time to call Merc.

    I didn't know that you were an old merc man. I should have realized given all the posts I've researched with your name on them.

    Thanks for helping me follow through on this.

  7. #7
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    Default Re: Optimax spark plug change/Why?

    LOL

    You could ask six different engineers this same question and get six different answers!

    But it always come down to MONEY, the bean counters at the corporate level have determined that Merc can buy the newer plugs from NGK in quantity for less than the old one.

    That AND specifying the more expensive plug, causing NGK's sale #'s on that unit to rise, sweetens the deal NGK gives to Merc.

  8. #8
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    Default Re: Optimax spark plug change/Why?

    I just contacted the service dept in Wisconsin and was told that it didn't make since to mix and mingle the two different plugs. The iridium plug burns a little bit differently ("crisper" he said) and requires a different gap. As to the service bulletin he wouldn't comment and didn't seem interested in why service bulletin would say it was ok to mix the two or why there was no mention of gap changes if you did.

    It still seems to me that merc has put out a service bulletin that does not adequetly address the situation. My inclination is to follow this to the ends of the earth but since it does not impact me I guess I'm going to have to let it go.

    Thanks for going this far with me.

  9. #9
    Rear Admiral JustJason's Avatar
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    Default Re: Optimax spark plug change/Why?

    CharlieB hit the nail on the head.
    With spark plugs, on any engine, Ideally you'd have the gap as large as possible. But the bigger gap you have, the more voltage you need to fire the plug. Merc makes rolling line changes all the time for hundreds of reasons. Some for money, some for product reliability, some for product performance... so on, and so forth.
    It also take more voltage to fire off a platinum or iridium plug, than it does a standard plug. If merc feels that their ignition coils can reliably fire a different plug, a bigger gap, platinum or iridium, then they will make a line change.
    If merc gets a better deal on 1 plug or another, and if it will not adversly effect performance.... they make a line change.
    Maybe the guy you talked to didn't know why there was a service bulletin in the first place. Merc as a company has had thousands of service bulletins over the years, for thousands of different reasons. You can't expect 1 guy on the phone to know them all.
    Sometimes I pretend I that I don't know what makes sense and what doesn't. I just follow what 10 engineers decided to put in a service bulletin.... and I usually don't have a problem.
    just because you found it that way... doesn't mean it's supposed to be that way.

    Part of diagnostics is spending time figuring out not only what the problem is, but also sorting through what it isn't.

    The older the engine is, the chances of it having more than 1 problem goes up exponentially

    Boating has always been a rich mans hobby. Buying a new boat gets cheaper every year, but the maintenance, the repairs, and the overall cost of ownership of a boat has never gotten any cheaper.

  10. #10

    Default Re: Optimax spark plug change/Why?

    I just changed the plugs in my 04 150 optimax. When i got to the no. 2 cylinder,. The electrode on that plug was just about burned up and the insulator had a green tint on one side. All the other plugs were the same. I use the NGK Iridium IZFR5G. What would cause that plug to be different? Thanks

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