Oil on spark plug threads

I replaced spark plugs at 143k. Driver side were all normal however passenger side all four plugs had oil all the way up threads. Side note when motor calls for power at high rpm a knocking or rattling sound can be heard from inside cab. Any help would be greatly appreciated. TIA

 

valve cover gasket

 

This ^^^And possible timing chain tensioner. Although these motors are very noisy at sustained upper RPMs.

 

I was thinking something to do with the timing chain

 

Did you install the prior set of plugs or have them done elsewhere? What was the tension when you took them off? The whole side is interesting and wondering if they were installed with in a series with only moderate torque and the installer went on to the other side and got confused in the process.
It’s unlikely that a whole bank of cylinders would individually develop problems at once, so I vote with the camshaft timing/tensioner or chain issue.

 

I agree, very strange. To my knowledge they were factory plugs. I bought the truck with 25k so I highly doubt someone changed them.

 

I just looked at mine as well today and found 2 on the passenger side had a small amount of oil on the threads as well as one in the middle on the driver side. I’m at 72k. First two in the pics which were on the passenger side middle two plugs had oil on the threads. Not sure what plugs should look like at 72k, but they all look pretty worn.

 

The seal on the outside is most important IMO. The black on the threads is bound to occur over time but you don’t lose compression. I had thought that a bit less of a seal on the gasket ring might allow a minuscule amount of seepage that would draw gasses into the threads, but I have seen this dark color often without other engine issues.
The rattling at high rpm was more of a concern to me. Sounds like the truck is running well other than that. There is a lot going on under the hood at high rpms and wondering if the source might be outside the engine itself.
I am amazed at how long plugs last in these new cars. I HAVE to change the plugs in my old case tractors every year. On 10% ethanol they start running like crap and quickly die. I imagine all kinds of issues Then I pop in new plugs and they purr like a kitten.

 

Have you had the valve cover off, ever? Maybe for a cam tower leak?
There are 4 donut shaped seals that seal off the spark plug tubes from the valve train. Lots of people will re-use them.

 

Valve covers have not been off

 

Well just like any seal they can go bad even if the valve cover has never been off.
Just my 2 cents.

 

For sure, just answering your question. Trying to get as much accurate feedback as possible.