I just changed my plugs yesterday and found that 2 of them on the driver's side had quite a bit of black build up and oil on the threads. Has anyone else experienced this? My truck only has 18k miles; so I didn't expect this. Could it be oil being sucked in through the intake? I do see some oil residue in the plastic intake tube and in the throttle body behind the butterflies.

 

I wouldn't worry about that, especially the sooty plug tip. These engs. run pretty 'rich' and if you're doing a lot(?) of around town driving, that's probably 'normal'. As to the "oil on the threads"; I don't think there is enough of the plug in the combustion chamber to get oil on the threads???

Dan