I just replaced the spark plugs on the AJ16 and I have posted a picture of what it looked like...

The car has 60,000 miles and I'm not sure if the plugs are original or not.

No dielectric grease was used on any of the boots.

Is this normal? I've never seen the ceramic cylinders get charred like this.

 

If it's any help, I had the same thing on a few of the plugs that came out of an XJR. I figured it was due to slight pressure leakage around the valve cover combined with high heat. The "hemi" style plug location seems to cause darkening around the plug when they are run for extended periods before changing? I have noticed this darkening on Toyota engines as well that have recessed plugs, so I tend to think it is more or less common. I'm thinking it doesn't take much oil vapour to cause this sort of thing. Since replacing the cover gasket, I have not noticed any further darkening, but it's early days yet.

Just a thought.

 

mine looked the same. especially on the white part of the plug. That could be old anti-seize in the threads. I think some people use it

 

Thanks.

I use anti-seize and dielectric grease.

Have you guys used the grease at the ends of the coils?

I have to admit, swapping out these plugs is pretty freaking easy. Swapping them out every 30K will hardly be a chore.

 

This needs to be a major sticky due to number of complaints about the corona discharge (I get this after a night of Mexican beer)

Maybe a little salt and lime with the RC12YC would cut down on the problem!!!

bob gauff

 

Now that was funny!

Me too, by the way.

 

Thanks for the reminder Bob.

I remember thinking my plugs were experiencing blow by because of the discoloration...exactly like Vee's photo...until your info set me straight. Thanks!

 

Excellent! Thank you so much. I didn't think I'd be able to get a definitive response like that on this subject.

I wonder if that has anything to do with Champion spark plugs being perfectly suited for these engines. Perhaps other plugs allow the blow to reach the tip of the plugs...

 

No, almost all plugs do that on almost all engines. The AC Delcos have always done that on my GM products.

 

Interesting! Kinda like the collection of debris around an air ioniser. I guess I was somewhat close to the right answer.

Well, I'm off to build up a massive corona discharge!

 

Yes, I had this too - only not as dark.