One of my spark plugs keeps turning black. I assume it is oil. What is causing this? Is this a head problem or a engine block problem? How do I get it corrected?
Assuming it is burning oil then it could be the inlet valve stem oil seal or worn piston rings. It's easier to do the stem oil seal than it is to get to the rings. If you take the head off and the back of the inlet valve head has baked on oily carbon deposits then chances are the plug fouling was caused by oil being sucked down the inlet valve guide.
If the back of the valve is clean then your rings are most likely to blame.
Is it greasy black (oil) or suity black (carbon build up)?
If it's just carbon and it's on your #1 or #6 cylinder this is normal for these engines because of poor air flow.
I just live with it and don't know how to cure it, but maybe someone else here with more knowledge does.
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