why slightly burnt spark plug at 65,000+ miles?

[drexx]

09Jul2005 (UTC +8)

My stock factory spark plugs, Denso SK20R11, has three of them slightly burnt at edge of the ceramic parts. It doesn't look as bad as this, only about 1/5 as bad, as this pic I saw on the 'Net (it's not mine!):

Mine's a 2001 UZJ-100 with more than 65,000miles travelled. I wonder what caused this? Otherwise the spark plugs look very normal as defined in Denso's website. http://densoiridium.com/howtoreadusedplugs.php

I'm currently invesigating this, then checking engine compression, checkin valve clearance, then putting the TRD Supercharger

 

[spressomon]

My OEM plugs, at 70K, had this discoloration...although not near as pronounced/dark...

 

[NMuzj100]

Better explanation of the spark plug corona phenomenon

Click Here - also from denso

NGK on the Corona

Nothing to worry about. Supercharge that beast.