Spark plug change interval

Discussion in 'General Discussion' started by Paul G, Jan 13, 2020 at 11:39 AM.

Car Parts
  1. Paul G

    Paul G Full Access Member

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    Factory change interval is 15000 miles on the factory Champion RC12ECC plugs. At that mileage the plug gap is opened up and they do show wear. They need to be changed. I have been using NGK ZFR5N V power plugs, at 15000 miles the gap has opened, but they are showing almost no wear. I have 2 sets of them like this. I am thinking of just cleaning them, re-gapping, and using them again for another 15000 miles.

    Has anyone re used these NGK plugs after re-gapping them?
     
  2. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    I know the NGK Iridium Plugs have a 2-stepped firing point.
    Once the thinnest part of the firing-tip wears down (it gets to a wider area below it), the plugs are done.
    The "problem" with most plugs when they are worn is they still fire BUT the spark is weaker and later (timing wise) and although there is no misfire, the fuel mileage tends to drop off; sometimes quite dramatically.

    If that V area fires easily, it may not once that is worn away, I don't know.

    The plugs are cheap enough and not $15.00 each like the ones I have to use. I'd turf them and buy new ones.

    I'd phone NGK Tech and ask them what they think about regapping.
     
  3. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    NGK Iridium= The plugs I use.
    NGK "V" style= The plugs you use. :)
     
  4. Paul G

    Paul G Full Access Member

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    Yes they are the V style. The v groove in the electrode is still visable and looks very good yet on these 15000 mile plugs. How often do you change the Iridium plugs?
     
  5. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    I don't know yet.
    There is only 6500 miles on them.
    I'm using aftermarket heads and more compression so I'd be happy with 15,000 miles.
     
  6. GSJake

    GSJake Member

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    Wait.. we only get 15K on a plug change???
     
  7. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    The "problem" with modern ignition systems is they channel power directly from Thor.
    There has to be something VERY wrong with a spark plug these days for it not to fire at all.
    Years ago, engine misfire was the #1 indicator that it was time for a tune-up.

    Not the case anymore so as long as the engine is running, guys seem to forget about plug change intervals.

    The new('ish) Hemi engines have 16 plugs and the non-D.I.Y. owners aren't anxious to have someone change spark plugs. The dealers charge $700.00 to do that in Calgary, Canada. Plus the mystery charges like "shop supplies" and environmental fees for Greta to save the planet from our stupidity. ;)
    (It's been recently suggested we switch to electric missiles as they are WAY better for the environment...)

    So, I've owned (4) 5.7L Hemis so far and if the plug changes are left too long, they drop off pretty fast in the fuel economy department.
    They still seem to run fine but the plugs are done.

    If a plug needs (for example) 16,432 volts to fire, that is right when it will fire.
    If you purchase more powerful coil packs they provide more reserve.
    So, if your newly purchased coil is rated at 75,000 volts, it doesn't mean every plug will now fire at the rated 75,000 volts.
    The plug we were talking about still fires at 16,432 volts with or without upgrade coils. As it wears, the plug will require more and more voltage before the spark jumps the gap and lights the fuel and air.

    The vast majority of our truck engines will do just fine with the o.e.m. ignition systems.

    The ORIGINAL Hemispherical combustion chambers are notoriously hard on plugs as there is NO natural squish/quench to cool them down. With the old dual-point ignition system I had on my 426 Hemi (even with a 40,000 volt aftermarket coil), they wouldn't last more than 1500 miles before starting to misfire and fart around at 6500 rpm. Changing out to a Chrysler electronic easily extended plug life by 5 times what it was with the anemic dual point. The plugs themselves still wore out fast compared to newer engines.

    Anyway, back on point: The plugs will still fire, the engine will still run quite well. IF you are fussy and/or trying to optimize gas mileage and horsepower, change your plugs when the gas mileage starts to drop off and/or the gap has grown rather large (because they are worn out).

    Champion used to make a spark plug flashlight (mine still works from 1972) so you can have a proper look at the spark plug (particularly the ceramic). Without one, have a look at the firing tip with a decent magnifying glass under good light. Compare it to the new spark plug you just bought. If the firing tip is considerably worn, change them all. Keep track of how long they last and that is your change interval.

    Another ramble on my part but it is 31 degrees below zero right now and there isn't much going on.

    Ronnie
     
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  8. GSJake

    GSJake Member

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    Thanks Ronnie for the info as always good stuff!

    Why 2 plugs per cylinder in the new Hemi?

    I should expect only 15K on the factory champions?
     
  9. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    (2) plugs for a better burn (lower emissions) and better fuel economy.
     
  10. THEWELSHM

    THEWELSHM Active Member Supporting Member

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    Wow I put a set of Bosch multi fire in , and didn't change them for 80k miles no issues....

    thewelshm
     
  11. Paul G

    Paul G Full Access Member

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    I just checked the gap on the NGK's and put them back in. They are holding up well. Much better than the factory champions did.
     
  12. rottenronnie

    rottenronnie Well-Known Member Supporting Member

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    I've never been a big fan of champion plugs.
     
  13. MGVIPERTRUCK

    MGVIPERTRUCK SPG > MPG Supporting Member

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    ::thinking it's time to change my plugs::