I removed what I think are the original plugs today (37K miles on a 2002 XJ8) and I found a small amount of oil on the threads of 2 of the plugs. As I peered wayyyyy down into the head I could see just a few drops of fresh clean oil.

I'm assuming this means that there is a small valve cover gasket leak...yes?

The plugs I removed were NGK [U]R [U] PFR50 11E and were gapped at .040 Are these likely factory originals??

I replaced them with NGK Iridium IX BKREIX-11 stock # 5464 gapped to .035, drove the car to test and it ran flawlessly, so I didn't mess anything up

I'm attaching a photo of the plugs-what do these tell you?

Thank you in advance for all your help

 

The factory plugs are to be replaced at 100K miles in the NA 4.0 engine.

The originals are the NGK plugs you removed.

bob gauff

 

Thank you for your fast help on this and my other "what is this part" post.
I thought I would change the plugs since the plugs were in the car 10 years. I was also curious to find out if they would be easy to remove, which they were.

So I should be able to go 100K miles on this set of iridium plugs then?

 

You probably could have gone 60K more miles on the originals.

I replaced my 1999 XJ8L plugs with Jaguar OEM (I get wholesale price from the dealer)
at 97K miles when I replaced all the timing chains/tensioners.

I don't know about the Iridium plugs because I never tried them.

bob gauff

 

Yes !

Oil leakage into the plug recesses is commonplace on many DOHC engines where the plugs go down tunnels formed by the cam cover and cambox. Normally a new cam cover gasket solves the problem.

 

Where should I buy these from? I live in the San Francisco Bay area.

thank you