oil found on spark plug threads

[snowshew]

Hello,

I have a 2.7 Ecoboost which had a misfire in cylinder 6. This is the plug I pulled from that cylinder, note the oil on the threads. The engine/spark plugs had 19.5k miles on it. I replaced all the plugs with the updated part number plugs (SP594) and cleared the codes. The misfire has gone and not returned (yet?). I drove the truck about 350 miles and rechecked the plug. There is some oil on the threads but not nearly as much as in this picture.

The dealership originally found the oil on the plug when searching for a coolant leak and had also noted the misfire in that cylinder. They found oil on the plug, presumably wiped it off and reinstalled it and told me about what they found. I had them finish the coolant work and took the truck home and changed the plugs. I was working under the assumption that I had a spark plug tube seal leak. There is no blue smoke and no oil use that I can detect, and the tip of the plug, though wet with oil, really only has the same amount of carbon as the other 5 plugs. When I recently re-checked the plug I found no oil whatsoever in the spark plug tube well. There was no oil on the ceramic of the spark plug and the coil boot was dry. I can find no evidence of oil having ever been in the spark plug tube well. Also, the spark plug tubes extend well past the tube seals and I can see no way for oil to go up and over the metal tube and down to the plug. I can see no evidence of oil where it should not be, coils, valve cover, etc.

Question: why is my spark plug threads wet with oil? I have been told that this might have caused the misfire that I had been experiencing (although I don't really understand how) and I am concerned that the misfire condition will return if oil continues to build up around the threads of the plug. I am completely stumped as to the source of the oil on the threads. I want this addressed under warranty if applicable but I don't want to spend a ton of money and time for the dealership to poke around; also, they don't seem interested in doing so. All theories welcome, thank you in advance.

 

[Plawan]

Well the first thing I’d think of is a leaking VCG or a bad tube seal but you say there’s no sign of that. The other possibilities are a clogged up PCV system, worn valve guides or worn or damaged piston ring.
I’d make the dealership fix it under warranty if it’s a mechanical issue. I’d they won’t look into it I’d have a non affiliated mechanic diagnose it and go back to the dealership with the information.

 

[snowshew]

A few extra possible data points: When the dealership found the oil they initially reported to me that they found "lots of oil in cylinder 6" and that they borescoped the cylinder but saw no signs of scoring, etc. I take that information with a grain of salt, but it may well be true. The engine does not run like there is a weak cylinder, the plug is not fouled and there is no smoke. I had an oil analysis performed and there is nothing abnormal. Certainly no iron in the oil.

As to a clogged PCV, would that not affect all 6 cylinders equally, and, even if it was ported especially into cylinder 6, would that not manifest as a excessive carbon on the spark plug? Similarly for the rings and valves, I'd expect a lot of blue smoke on start up for sure, as well as a fouled plug.

Yes, the valve cover and down the tube looks to be bone dry. There was no indication of oil having ever been on the coil boot or the original spark plug.
Thank you for the reply, I remain stumped.

 

[Marcozi]

A couple of things can cause the plug threads to have oil:
- bad valve cover gasket or gasket that separates the plug well from the oiled sections of the cylinder head
- spark plug wasn't sufficiently tightened when installed
- bad sparkplug sealing washer.

 

[snowshew]

Is there a lower seal between the metal tube and the head or is that pressed into the head. In the case of this engine I really don’t see how a bad upper tube seal could be related to oil on the plug, the metal extends well above the seal and valve cover. It looks to me like the oil would instead run down the valve cover. If plug were too loose, would that oil all have been present in the cylinder if everything were correct? I would not have thought the underside of the head would be exposed to oil.

Thank you for the input!