What would cause a spark plug to look like this?

Gawd danged need to do something about that coil too clean it with some electrical contact cleaners and berryman spray something I would replace that nasty thing probably.

 

Do you know if that plug was original, or, if not original, where it came from?

 

Those are the IK16 I've run a few of those and it's easy to get those in fakes too You have to be careful I even still have some of the boxes from those those are they're not the TT's they're the IK's I can't remember what the deal is with the IK designation nipondenso over the years have changed all their prefixes and whatnot.

 

Might want to look with a borescope at the condition of the cylinder; sometimes the question with those fakes is where did the bits go that fell off?.

 

What You should make it to 450k pretty easily unless you're HV battery craps out and then you just rebuild or get a rebuilt one I get them from his rebuild guy for 550 a pop I just exchange at his shop I hand him one he hands me when I drive off and maybe the brake actuator. But those are like the two most expensive things if the CM monitor or speedometer goes out you want it fixed correctly you get the one from the people at Texas hybrids it's like a buck 75 after all said and done or you can try to put three capacitors on yourself or what have you but that car should last almost another 300,000 All of my Toyota has made it to 400 450 all of them. I've been driving these things 45 years actually a little longer now. Anything after 2010 maybe not so much seems planned obsolescence and keen manufacturing and marketing is taking over and well they're just not what they were. I can make 2009s last me until the big change whenever that comes could be another 20 years '09's will last me no problem.

 

1. You'll need a valve cover gasket kit to fix that leak into the spark plug well.
2. What happened to the ground electrode for that spark plug? Is it still bouncing around in your cylinder or has it been ejected out?.

 

Whatever goes into a cylinder from a spark plug hole is gonna be in there until it happens by sheer luck to bounce out an open valve into the exhaust or intake. The oil pan isn't a place it'll end up, unless it gets pulverized first finely enough to get past the piston rings. (Or, a big enough piece of debris might get there by busting through a piston, but I think that'd have to be bigger than a spark plug electrode.)

 

Replacing valve cover gasket is what I'm seeing... You likely have an engine that didn't get an oil change very often. Maybe an engine flush before an oil change would help, as well as changing oil a few time with more engine flush in next 10K miles. I wouldn't be too concerned about the other problems people are talking about unless it still runs rough on a new set of plugs.

 

Whenever I've pulled a plug from a failed valve cover gasket there's fresh oil on the inside of the plug as well as on the outside. And I agree that it doesn't make sense that the oil could leak through the threads, but that's what I've seen. I suspect there's a logical explanation for it though.

 

One of the o-rings that goes around the spark plug wells is just compromised and it's leaking no big deal it's just a piece of rubber not real special when it gets hard and ate up from thousands and thousands of miles it's tends to shrink and oil will seep in there now you're going to slap a new $9 fell pro gasket down and not going to give a crap about it anymore. Then you could take a magnet on the end of an extension a pickup tool and stick it down the spark plug hole with the spark plug removed and see if you pick up any pieces of metal when you swirl it around in a little bit You could even bring the piston up to the top so if the piece of garbage is way down in the bottom it'll now be closer to you you know the little magnet on the gooseneck is what we want to be using here You rotate the engine around by the crankshaft pulley with a screwdriver stuck in the number whatever hole it is and watch the screwdriver raise up out of the hole to indicate the piston is at top dead center any little pieces of nonsense down in there should now be real close to you stick the gooseneck magnet in the whole and running around carefully pull it out of the hole see what you got do it once or twice if you get nothing no worries.

 

That gasket's probably never been replaced so it's long overdue It is not a permanent part keep that in mind

 

Looks like the cover gasket and spark plug well rings are one piece, under $25 CDN all-in, for me in western Canada:

Buy Genuine Toyota 1121321011 (11213-21011) Gasket, Cylinder Head Cover. Prices, fast shipping, photos, weight - Amayama

Part no: 11213-21011