Here's why:
* Coolant in the cylinder: The presence of coolant on the spark plug indicates coolant is leaking into the combustion chamber of cylinder #2. This is a serious problem.
* Head Gasket Failure: The most common cause of coolant leaking into a cylinder is a failed head gasket. The head gasket seals the combustion chamber from the coolant passages in the engine block and cylinder head. A breach in this gasket allows coolant to enter the cylinder.
* Cracked Cylinder Head or Block: Less common, but possible, is a crack in the cylinder head or engine block itself, allowing coolant to leak into the cylinder. This would usually involve a more significant coolant leak than just fouling one spark plug.
Other (less likely) possibilities:
* Cracked cylinder: While less likely than a head gasket issue, a crack in the cylinder wall itself could also allow coolant to enter. This is usually accompanied by other significant symptoms.
What to do:
Do not continue to run the engine. Driving with coolant in the cylinder can cause severe damage, including:
* Hydrolock: Coolant in the cylinder can prevent the piston from moving, causing significant damage to the connecting rod, crankshaft, and other internal engine components.
* Internal corrosion: Coolant mixed with combustion byproducts is highly corrosive and can damage internal engine parts.
You need a proper diagnosis. This likely requires a compression test (to check for cylinder pressure loss indicating a leak) and a visual inspection of the head gasket (which often requires removing the cylinder head). A mechanic specializing in automotive engines is recommended to diagnose and repair this issue.
