A thicker oil, such as 10W-30 or 10W-40, is less likely to seep past worn seals and rings than a modern low-viscosity 0W-20 or 5W-30. Primary Causes of Oil Fouling The presence of oil is almost always a symptom of an internal leak.
Common Causes of Oil on Spark Plugs
Low compression in one or two adjacent cylinders strongly suggests failed piston rings, while a drop in pressure when the throttle is snapped closed points to worn valve seals. This condition is rarely random; it is a diagnostic clue that reveals specific problems within the cylinders, ranging from worn piston rings to incorrect oil viscosity.
" A second major cause is worn valve stem seals, which fail to keep oil pooled in the valve guide from trickling down the stems and into the chamber, particularly when the engine is off and the car is sitting. However, if the piston rings are compromised, a full engine rebuild or replacement becomes necessary to restore proper sealing and compression.
Worn Valve Stem Seals Let Oil Leak Onto Spark Plugs
Drivers will often notice a thick, blue or gray exhaust smoke billowing from the tailpipe, especially during startup or acceleration. This intrusion physically blocks the spark, preventing the ignition of the air-fuel mixture and effectively turning the cylinder into a non-combustion chamber.
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