Spark Plugs Shouldn't Look Like That

The brown/black on the white insulator portion looks like carbon from arcing?  Am I way off base?

What might cause that?

Car is a 2009 Hyundai Sonata four cylinder with about 180K miles.  Plugs have about 90K on them and are Denso and iridium if that matters.

Looks like oil to me.  Leaky valve cover?

In reply to mikeatrpi :

Yeah that's coked oil

DWNSHFT said:

The brown/black on the white insulator portion looks like carbon from arcing?  Am I way off base?

What might cause that?

Car is a 2009 Hyundai Sonata four cylinder with about 180K miles.  Plugs have about 90K on them and are Denso and iridium if that matters.

That's normal for old spark plugs.  This may squick you out a bit, but what that is, is the traces of combustion gases that have been leaking past between the porcelain and outer shell for the past eleventy thousand miles.

Yeah.  Spark plugs don't seal the chamber 100%.  99.9999999%, yes, but that .0000001% of blowby leaves a stain on the porcelain after a while.

Knurled is 100% correct. Back when spark plugs were replaced every 10k we never saw this. Now it is always. These are normal for their age, no other problem is present.

Thanks, all!  I'll sleep better now.

Just to build on what Knurled said a bit, I'd expect to see that less on cars that spent their 100k doing all freeway miles and never shutting down (cop car?).   The biggest cause of that is the different coefficient of expansion for materials that make up the spark plugs..  You can create a solid aluminum plug that'll seal a whole heck of a lot easier than a plug made up of at least 3 different materials ("x"-clad Copper, procelean, steel, etc.). 

I'm sure they seal a whole lot better when they're completely warm, but there's a >200 degree difference between total cold and total warm that they endure every time the car is used from cold.

Yep... pretty normal. You didn't see it back in hte day because the spark plugs didn't last more than 20k miles. Now we're getting 80-100k between plug changes you get to see all sorts of fun things. 

TIL.