My BMW M3 E46 seems to be running rich on start and getting poor mileage so I pulled the plugs to have a look. I know how to read normal plugs but these are NGK Iridium plugs and I'm not sure how to tell whether these need swapping out. I don't know how many miles are on them.

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There are 3 others but they're all about the same. These seem okay to me, but then I've never seen this type before. Should I clean the threads up and re-gap them or replace? If there is a good chart for iridium plugs I'd love a link.

  • I spelled iridium 'idirium' in my title originally. Looks like it's gonna be a long week.
    – GdD
    Sep 27, 2021 at 16:21
  • I do know these aren't original, the factory installed dual electrode platinum plugs.
    – GdD
    Sep 27, 2021 at 16:26

1 Answer 1


From what I can find "iridium" means platinum with about 10% iridium as alloy. I doubt the plugs are causing a problem but they do not look good in my limited experience. I have pulled 2 sets of 8 after 100,000 miles and I could almost have mixed the old ones with the new ones I put in. One set was made in 1998 ( GMC truck ), one set was made in 2004 ( Nissan truck). No problems with either. I would replace them according to the manual; but since you have them out why not put in new ones. In the old days with leaded gasoline, cleaning plugs was worthless.

  • Thanks @blacksmith37, I just meant clean the threads rather than the electrodes. I probably will replace them with the oem style ones.
    – GdD
    Sep 27, 2021 at 17:53
  • Those plugs are fine and usually rated for 100k miles in many vehicles. Conventional non exotic tipped electrodes will wear down in a few thousand miles and require re-gapping often as they show visible wear, replaced as often as every 15k to 50k miles. There are other issues that may be due to a worn out t-stat, dirty maf sensor, clogged air filter, etc. This requires more in depth diagnosing and troubleshooting.
    – F Dryer
    Sep 29, 2021 at 20:01

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