Porcelain part of spark plug is BLACK

[JoeC5]

I dont know if this is good or bad. I am running NGK Platinum plugs. On the driver side, the one in the back, is all black (porcelain part). I check the others and they all all normal, meaning no discoloration. Whats going on. Is this plug generating too much heat?

 

[IAMCDN]

What kind of black - oily black or carbon black?

It would make me wonder why one is black and the others are not. I have changed many plugs that were black, and as long as they are not oily black, then it is normal (for older plugs).

 

[JoeC5]

Not sure, but is baked on there pretty good. However I did notice that right above the plug (valve cover), its is leaking a little bit. It is also on the exhaust manifold.

 

[Rhett]

Black generally means 1 of 2 things:
1) the engine is running rich, (meaning it's carbon) or
2) there is an oil leak (meaning it's oil crust deposits).

Most likely that plug is not running hot or else the porcelin would likely be burned white.

On a 4.0 OHV motor, the middle plug on the driver's side (plug #5) has been known for this. You say a little oil shows on the valve cover, so this is consistent...maybe there is a valve cover gasket leak. Often the tipoff is oil crust on #5 plug. Is the leak significant enough to where you have to add oil between changes?

 

[JoeC5]

Yeah, Its dripping down onto the exhaust manifold. Well you know what somethings looks like when there is oil on it. I dont have to add oil at all, but I still might replace the gasket anyway, just in case ya know. How difficult of a project would it be?

 

[Rhett]

Well, the black soot from carbon seems to be "dryer" whereas the black s*** from oil seems "greasier"...if that's any help to you. ehehe That's the best way I know to describe it with words..

Some people would tell you replacing the valve cover gaskets is not too tough, just remove all of the vac lines and things on the valve covers, then remove. For me it would take an entire weekend. I would suggest a Haynes or Chilton's manual for reference. Check on the "links" section here because I think there is a site listed there that has a section on the procedure and the best gaskets to use. I think the page is "Explorer Owners Maintenance Reference Page".