Welcome Guest - Sign Up today
Welcome Guest - Sign Up today
Store Links Mobile - Shop Now


1 of 2 < >


The iBoats Forums will be down for maintenance starting at 10 AM MST on 12/16/2017. The estimated amount of downtime is 3 hours (we are expected to be back up at 1:00 PM MST). Thanks for being a part of the iBoats community!
2 of 2 < >

Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old topics or hijack existing topics. Old topics of a technical nature are like a library book, Please do not write in them.

2. Old topics should be considered archives and used for reference only. Please do not reply to them.

3. Do not take over someone else’s topic (aka hijack) with your own question, even if it is similar. If you have a question that has not been covered to your satisfaction in the archives, it is always best to start a new topic of your own.

4. If you have a question for the original poster (OP) and the topic is over 30 days old, send the OP a PM, he may not even visit the forums any longer, or may not notice your question in the old topic.

5. By starting your own topic, you will receive the maximum number of views by forum helpers that may not even notice your question when it’s posted at the end of someone else’s topic. And those answers will be specific to your particular issue.

6. Please do not post to topics that have been inactive for more than 3 months unless you are the original poster. We have very active forums and any topic that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old topic.

7. Posting at the end of any topic is considered to be hijacking the original posters topic which in turn subjects the topic to be closed if it continues to happen thus not making it fair to the original poster in the future had for some reason he/she needed to return for additional information or provide an update of the problem solved which is always welcomed within a reasonable amount of time frame.

8. Please note that you should see a red banner pop up near the bottom of each inactive topic asking you not to reply to old topics. The Red banner will read: Please note this topic has been inactive for 90 days. For the best results, please start a new topic.

Thank you all in advance for doing your part in helping iboats run a smooth ship.

Additional forum rules linked below.
See more
See less

Optimax spark plug change/Why?

  • Filter
  • Time
  • Show
Clear All
new posts

  • 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
    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.
    Just because you can doesn't mean you should.

  • #2
    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
      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.
      Just because you can doesn't mean you should.


      • #4
        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
          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.

          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
          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
          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)
          Just because you can doesn't mean you should.


          • #6
            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.
            Just because you can doesn't mean you should.


            • #7
              Re: Optimax spark plug change/Why?


              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
                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.
                Just because you can doesn't mean you should.


                • #9
                  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 does not mean it is supposed to be that way.


                  • #10
                    Sign up today
                    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