Spark Plug #4 oil fouled.

IROD

MEMBER
1999 FORD F-150
V8
4WD
AUTOMATIC
155 MILES

Number 4 spark plug keeps getting full of oil and engine light comes on. I've cleaned and changed the spark plug once and within one week spark plug became oily again and the engine service light came back on.

Ring issue or valve guides? How do I know where the oil is coming from?

Thank you.

Ivan

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

The best way to know if the oil is coming from the rings is to use a borescopre and see what the cylinder looks like through the spark plug hole.

If the plug is coated in oil but the rest of the cylinder doesn't have much deposits or looks clean then it is a valve guide seal.

If not then the rings are move likely the issue. Then I would just remove the head and get a closer look before you pull the motor out.

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust

Below you will find a chart as to what the plug should look like to confirm this is oil.

I also attached the process on how to replace the seals because by the sound of it, there is not much oil which could just be a leaking seal.

Please let us know what you find with this. Thanks

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