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  1. #1
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    Merc 4S 150 plugs - Precious metal "dot" Iridium

    Merc 4S 150- 2017- 180 hours- plugs are suppose to have a precious metal "dot" on the electrode. If gone - replace plugs. I pulled plugs to apply anti-seize to threads (per manual on salt water applications) Check gap. All 4 - there is no visible dot. I did not Clean electrode with sand paper or anything. Over all appearance nice tan- good condition. Motor running flawless. Is Iridium actually gone? Should it be at 180 hours?
    Just checked price- less $5 each. This actually a fairly common plug- automotive in applications. Seems like an obvious - just change them- except #4 is tricky to get to- risk of strip or cross thread.
    Suggestion to others- go ahead and have new plugs on hand- put them in-

  2. #2
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    No issues, no problem. I've had vehicles go 160k miles on factory plugs.

  3. #3
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    I wouldn't swap them but if they are out spend the $20 and replace them. A 5/8 deep socket and 1" extension makes number 4 very easy to get out. Just make sure and start it with your hand. Also stand in front of the motor and lean over the top if possible.

    As a rule of thumb on non performance 4 strokes I do plugs every 3 years when we do the pumps and t-stats. As recommended by merc


    Also NGK claims there plugs already have a super special coating that keeps them from siezing..... pick who ever you believe on that.
    Last edited by RSWORDS; 04-13-2019 at 08:30 PM.

  4. #4
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    Don’t remember if iridium have the dot. Platinum normally do. Only affects waste spark where the plugs use resistance in the platinum to create a +- plug so strong spark goes to correct cylinder. It would run rough if it needed it.

  5. #5
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    I ran the standard automotive plugs in my 2013 Merc 150 4-stroke. Changed them every 300 hours. Motor had 2,800 hours on it when I sold it.
    Aaron
    Fountain 38TE, quad 400 Verados
    Talon F20 Flats boat, 250XS

  6. #6
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    Napa can get you the FR iridiums for about 10-11 bucks ea. 1/2 of dealerprice. Same exact plugs

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

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