NGK laser Iridium spark plug discoloration

[penz08]

Good day folks,

Today I pulled out one spark plug on my 2.0 Skyactiv engine to see in which condition the plugs were by curiosity.

These plugs have around 25 000 km on them only, but to my surprise I noticed this very dark brown discoloration at the bottom part of the white core. The actual tip of the plug looks good with a bit of soot on it.

Is that brown discoloration something to worry about? (see photos).

 

[AutoMechanic]

That’s called corona stain. Nothing to worry about. It’s just from the oil particles that were above the plug when installed. Doesn’t affect anything.

 

[paulo57509]

It's normal. However, what the arrow is pointing to is not.