I recently did a tune up so today i wanted to check a few of the plugs and see how there burning. All looked super clean. But cylinder 5 had oil on the spark plug threads. The plug electrode looked fine but the bottom rim of the plug had some black. What does that mean??

 

Hadda go find a couple of things... ok, here we go.

The '98 has a 2v 4.6L in it, with spark plug wires and two coil packs. The spark plug is bolted in the top part of the head. It's possible that there is a bit of oil leakage around that particular spark plug hole from one of the nearby gaskets, or someone used oil to help the plug go in. Now, if you were talking oil on the electrode, then yeah, blown valve seal or piston rings.

But it doesn't seem that's the case. If it's not the oil was used to help the plug go in, then oil that's leaked out seeps and pools in the little hollow where the plug lives and wicks it's way into the plug. Either way, the oil at the bottom and gets burnt when it hits the combustion chamber during engine running, which is why the tip is fine.

At least, that's my guess.

I'd run it, and then check in about 5K and see where you're at with things.

 

Thanks man for the advice-if it's a seaping gasket then it's not that bad yet-the car dosnt smoke so I will keep eyes on it.

 

If it's not on the electrode and only on the threads you should be okay. (In terms of ring/piston damage or blow-by.)