I changed out the spark plugs on my 2004 LS430 with 111k miles on the clock last Wednesday evening. From what I can tell going over the service records the plugs had never been changed before this and the engine operated normally and smoothly.

For the most part, the replacement process went fairly smoothly. I picked up a couple of tips from some of the other threads that helped me along the way. I found that using a short needle nose vise grip pliers to squeeze open the latch on each wiring connector running to the COPs made them come off easily.



I did notice that on three of the spark plugs that I removed, cylinders 4, 5, and 8, that there was a significant buildup of dried up oil surrounding the base of the plug where it seals the combustion chamber. It was so bad on cylinder 8 that when I pulled the spark plug out of the socket it was coated in oil. The other thing I noticed was that all three of these plugs did not require much force to break them loose from the engine while several of the others were much tougher to break loose and then remove.



Cylinder 7 - 5 - 3 - 1



Cylinder 8 - 6 - 4 - 2



Oil on end of COP cylinder 8 after removal from cylinder



View of plug from cylinder 8 after removal

So my question is what is the root cause of this problem? Right now I'm leaning to it being an exhaust blow-by problem because of the way those three plugs came out so easily but I'm having a hard time believing that Lexus put three of those plugs in there loose. I have seen some threads where people have reported having leaking valve cover spark plug seals. If this was the case I guess I would have expected to see much more oil in the spark plug chamber than I did and I would have expected those three plugs to have been as tight as the others.

If it's a blow-by issue I guess there is nothing I'll need to do at this point. I'm pretty sure I've got the new ones installed properly and I guess I can look at them next year sometime to checkup on them. If it's a bad valve cover seal though, I'll need to order some replacements and get them in there.

Comments???

 

It's probably just the spark plug tube seals in the valve cover. They get old and let some oil slip by into the tubes, which will pool around the plug and can infiltrate the threads.

 

Not blow by.

You just need valve cover gaskets and spark plug seals. Pretty much routine at 111,000 miles.

If you don't change out the gaskets and seals, you run the risk of shorting the coil on plug and then you will need at least one of those. Better off to get her done otherwise the dealer will talk you into replacing all of them.

By the way, the real reason that you change the plugs at 60,000 miles is the ease of removal. As you found out the plugs are quality pieces and will easily last more than 100,000 miles, but as you also found they get to be harder to remove. Strip the threads and you have big trouble. Some aluminum heads are notorious for stripped threads.

 

+1 on the above ^^^ it's the seals.