Fouled spark plug in one cylinder (only)

Beginning a year ago, began seeing an increase in oil consumption:  Then suddenly, severe misfiring.  Inspection revealed that spark plug B in cylinder 4 was very heavily crusted/covered in Oil. Replaced plug and all wes fine... for ~ 4,000 km.  Then again, after only about 4,000 km, problem reappeared. Changed plug again, but this time, plug was dreadfully encrusted with oil/carbon.  (Spark plug A - in the same cylinder, gets much less so). 

To me, it seems that this suggests oil leak is from valve or something related to valve, (guides??)  rather than cylinders, rings, etc. Does this make sense? If so, is it recommended to first verify by doing a compression test to rule out the cylinder block, rings etc? And if yes, short of removing the heads, any way to verify the likely culprit? (  The car is excellent in most other ways, so any thoughts or strategies would be appreciated, BEFORE I go down the wrong road)!    With thanks






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MercedesMedic made a comment.
6 months ago

I haven't seen that many M112 engines with these kind of problems. How many miles on the engine? What oil do you use?

It could be from any of the items you mentioned. My guess is that this is valve guides as well. If it was head gasket both spark plugs should have been getting wet.

Rent a compression test kit from your local auto parts store and let us know what readings you get.

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Sthong1221984 made a comment.
6 months ago

Some possible answer to your question are already mentioned. I think you need to replaced valve cover gasket because of the problem from the spark plug.But It's better to do compression test to determining the mechanical condition of an engine. Measure compression pressures of all cylinders with compression pressures of all cylinders with a compression gauge.Then compare them with each other and with the manufacturer's specifications for a new engine.This provides an accurate indication of engine condition.


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abusufyan made a comment.
6 months ago

I think you got the right information about your issues. Do you have any other question for us?


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