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While inspecting the front 3 spark plugs (bank 2) on a 2GR-FE (2009 Toyota Venza), I noticed the spark plugs have oil along the entirety of their threads.

There was no oil pooling the the spark plug tube or on the ignition coil packs (just a few drops/smears here or there).

There was wetness at the spark plug tube seals and when I blew it out with an air compressor, some oil droplets splattered everywhere.

There is no perceived drop in oil level between oil changes.

Seems not ideal, but does it look like it's ok to forgo opening up the valve cover(s) and replacing spark plug tube seals for now? Since there was no pooling I'm thinking it could be a slow leak due to age.

Pics:

Some oil glistening on spark plug tube seal at valve cover, and a drop of oil at the spark plug, but no pooling: enter image description here

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Oil residue on seat and threads, with spark plug removed: enter image description here

Spark plug for cylinder #6: enter image description here

Spark plug for cylinder #4: enter image description here

Spark plug for cylinder #2: enter image description here

Just for fun, endoscope images from inside the cylinders:

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EDIT: Pics of cylinder walls and cylinder head taken with a 45 degree mirror in front of the endoscope. Only the middle 1/3 crescent in the images is relevant.

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If the valve cover gaskets are leaking, then there will be oil pooling in the bottom of the spark plug well. That's not happening and so that's not where the oil on the threads of your plug is coming from.

In this case it certainly appears to be coming up from the combustion chamber. The two most common ways of oil getting in are:

  1. Leaking intake valve guides which allows oil to leak from the cylinder head, down the stem of the valve, and into the chamber.

  2. Leaking piston rings that don't properly scrape oil from the cylinder wall and allows oil to remain on the cylinder wall as the piston does its down stroke.

In either case that oil is compressed and forced up around the threads of the spark plug. You also get the carbon buildup you are showing on the top of the piston.

It's possible there is some oil leaking into the well around the valve cover gasket but to my eye that doesn't appear to be the main source of oil here.

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  • Interesting thoughts. Though wouldn't oil getting into the combustion chamber result in oil burning? No drop is noticed in oil level. And to my untrained eye, the carbon buildup on the piston and spark plug colors look normal, no? Wouldn't oil burning result in more carbon buildup and spark plug fouling?
    – adatum
    Aug 20, 2022 at 16:48
  • Come to think of it, I did notice some oil pooling in the intake plenum around where the PCV hose connects, while cleaning the throttle body previously. I did clean the PCV valve and it seems to function fine, but there does seem to be a certain amount of oil that makes its way past it. Again, no loss in oil level is perceived on the engine oil dipstick.
    – adatum
    Aug 20, 2022 at 16:52
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    Oil doesn't burn as readily as gasoline so you get the characteristic blue smoke and also liquid oil forced up into anywhere it will go by the pressure. Oil in the intake plenum is pretty typical mostly from the PCV system. You get oily engine gasses into the intake and some of that oil condenses on the cooler intake.
    – jwh20
    Aug 20, 2022 at 17:11
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    I'm not saying you have a serious problem at this point, but you did ask how the oil was getting there. Some of it may be typical.
    – jwh20
    Aug 20, 2022 at 17:12
  • Your thoughts and insight are appreciated. There is no blue or white smoke. I've updated the question to add a more focused image of the oily spark plug tube seal in the valve cover, as well as several images of the cylinder wall and head. I wonder the they confirm or redirect your suspicions.
    – adatum
    Aug 20, 2022 at 18:01

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