Coming up on 100K, so figured time to change spark plugs. All 3 plugs on the right side had oil in the spark plug tubes. Checked AllData for repair, and it requires changing the cylinder head as they are not replaceable. AllData also states that it is caused by porous spots during the manufacturing process. Does anyone know if GM/Cadillac is making good on this known manufacturing defect out of warranty?
TIA
Glen
First you have to make sure the oil is not leaking into the tube as a result of the seals in the valve cover. As for replacing the cylinder head as a result, that's your call. If the oil source is not from the gaskets, then consider addressing the problem in a more realistic manner on a perfectly running motor. Get the RTV grey sealant used to seal the timing cover.
Remove the valve cover, get a good cleaner, like brake cleaner that evaporates as it cleans. Use it to clean around the tube joint at the cylinder head. Apply a vacuum to the tube (or not) and spray the cleaner into the joint again in an effort to try and draw it into the tube to flush out any remaining oil in the joint, then force the sealant into the joint around the tube, applying a little vacuum (or not) to help pull it into the breach area, followed by more packing for a complete seal at the joint.
I had two tubes do that with one a good bit more than the other which needed to be addressed. I performed the above procedure without using vacuum and without being as thorough as I normally would and so far it has held up well over a year. I didn't find out about the recommendation to replace the cylinder head until afterwards which I would not have done without a driveability problem anyway.
A few months back a 2012 owner with this problem insisted on replacing the cylinder head after the mechanic suggested the above instead. The mechanic posted here after the cylinder head replacement was followed by several engine codes that would not go away, even after removing the head and double checking his and the machine shop prep work and reinstalling it to no avail. That was 5 months ago and I still have not seen a conclusion in the thread associated.
I bet oil in at least one of the tubes is a common presentation on as much as half of these motors above 100k miles. I find it interesting no consideration is given to the possibility the glue job used on the tubes might not be all that great considering the leak appears to be the result of oil leaking past the joint where the seals are in good condition. Heck, you might be hard pressed to find a 100k mile 3.6L that doesn't have some small sign of an oil leak at one of the many sealant closed joints on the motor, particularly one of the bottom corners of the timing cover.
