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I have an oil leak leaking onto the coil side of the spark plug in cylinder 4 on my 2000 Toyota Tundra v8. This seems to be causing a misfire. The misfire is intermittent. I inspected the plug today and the spark side seems to be clean with no extraneous deposits. The plugs have about 15,000 miles on them. The coil however has a glazing of oil near where the top of the plug inserts. The oil is also wet around the white part of the plug near the insertion point. Any idea where the leak may be?
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The valve cover gaskets have a seal that seals the spark plug tube. They get hard and brittle over time and will leak oil into the spark plug tubes.
The tube is clean from the top all the way down to the problem area at the base. Wouldn’t the oil leak down from the top of the tube if the tube gasket is bad?
From what I could find online there’s only two ways that oil can get in there, either the top O-ring gasket is leaking (easy fix) or the bottom of the tube is leaking (huge nightmare fix). I was reading about a later model year truck so yours could be different but sounds like the plug tubes are screwed into the head and the threads sealed with sealant to keep oil out.
Sorry I can’t help much more than that, I don’t know much about the Toyota V8 engines.
Only thing I can suggest as a bandaid fix is to use a TON of dielectric grease and cover the white part of the plug with gobs of it, install the plug, put more gobs inside the coil tube and on the outside and install it, hoping they make a nice gooey seal that oil can’t get past to cause a misfire.
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