So, I pulled the spark plugs today to check to see how the engine is running. After pulling all 6 spark plugs, I've noticed there is a white deposit caked onto the spark plugs. I doubt this is normal operation, if anything this should indicate that the engine is running a bit off? But other than this, The car runs and drives fine, even under WOT, no indication of any issue or running rough.

We replaced the catalytic converters this week as well, The cats have white deposits on them as well, not sure what this is but i definitely don't want it to happen again to these new cats.

Spark Plugs

  • It would be unusual to have a cat without deposits, what makes you think anything is wrong?
    – GdD
    Jun 22, 2020 at 10:48
  • This page is good for comparing them to - championautoparts.com/Technical/Tech-Tips/…
    – HandyHowie
    Jun 22, 2020 at 11:15
  • They look like they have a small amount of ash on them, is it on both sides of the plug?
    – HandyHowie
    Jun 22, 2020 at 11:17
  • The catalyst itself was swapped due to it being clogged. This makes me thing the engine isn’t running right. Here is a photo of the clogged catalyst taken with a borescope i.sstatic.net/Nm6Ya.jpg yes, both sides of the spark plugs have deposits on them. Jun 22, 2020 at 12:22

1 Answer 1


Depending on the mileage on these plugs, I'd suggest there's absolutely nothing wrong with the way your engine is running. These plugs look to be in great shape. The small amount of deposits on the sides of some of the plugs wouldn't worry me at all. (NOTE: There is a decent chart on reading spark plugs I posted in this answer which may be useful to you.) The light tan deposits are quite common in an engine which is running just fine. They will build up over time, but are not a huge issue and one of the reasons you change plugs as a maintenance item.

  • Definitely. I would recon they were good as well. But due to the recent change in the catalyst and the way that it failed (catalyst clogged) definitely makes me think something isn’t right. We’ve replaced both bank catalysts, both look the same. Here is a picture of the catalysts material taken with a borescope i.sstatic.net/Nm6Ya.jpg Jun 22, 2020 at 12:25
  • @JamesVargan - Yah, that's definitely plugged, lol. However, the spark plugs have nothing to do with it. Replacing the plugs won't help you not plug the new cats. I'd suggest there's something else going on, like bad fuel, which caused your cat issues, but that's a different question. Jun 22, 2020 at 13:04

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