I pulled this spark plug from an engine that sat for a while. I’m wondering if any details regarding the running condition can by inferred from the picture.

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2 Answers 2


There's the portion of the spark plug which is tan, which indicates a good running condition (slight amount of NOx emissions, but otherwise not bad), though there are some slight amounts of carbon build up as well, which would indicate a slight rich factor. Either one of these two things could be because it has sat for the period of time. Overall, there is nothing which is telling me there is really any issue with how the engine was running. I don't see any large carbon deposits or even wetness, which would indicate it burns oil. It's not completely clean, which if this spark plug is typical of the rest of the cylinders, would mean to me there's no head gasket leak (if this is a liquid cooled engine ... assuming as much because I believe this is a Bosch Platinum +4 plug). All-in-all if we are just reading the plug, my suggestion is send it.

  • I was mostly concerned with blow by and indications regarding the health of the engine. All 6 spark plug share the identical characteristics.
    – Kevin
    Commented Mar 13, 2019 at 17:56
  • You can't (to my knowledge) tell blow by from looking at the spark plug. You'd have to pull the oil cap and look at what comes out while running. It's a general look see, but you'd know pretty fast if there was an issue. The spark plug won't tell you this information. Commented Mar 13, 2019 at 18:20
  • What about oil consumption by burning? Do you see any indication of that?
    – Kevin
    Commented Mar 14, 2019 at 1:22
  • @Kevin - As I said in the answer ... No. Commented Mar 14, 2019 at 1:23

The colour looks normal but the geometric offset of the centre electrode to the quad contacts looks a bit off. Thus the gaps could be sub-optimal. Replace it. Or take a better set of photos.

  • Gaps on Bosch Platinum +4 plugs are set from the factory. Due to the design, they intentionally look broad. The design of the plug has a thin sliver of platinum in the center of the porcelain. When energized, the electricity travels across the face of the porcelain, then jumps to the ground straps. This gives a broader spark coverage than would normally be possible if just taking into account the jump from the electrode to the ground strap (normal plug). From what I can see, the plug looks like it doesn't have many miles on it at all. Commented Mar 13, 2019 at 17:08
  • The left contact looks narrow , which results in a thin arc.,Is it symmetrical? Commented Mar 13, 2019 at 17:27
  • I think the way the image was taken makes it look off ... either that or you're seeing something I'm not. They are supposed to symmetrical and that's the way it looks to me (though I could be wrong). Believe me when I say, there's no way for a "thin arc" on these spark plugs. They're not designed to work like normal spark plugs do. Commented Mar 13, 2019 at 18:22

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