Spark Plug Tube Seals
Small circular rubber seals inside the valve cover that prevent oil from leaking into the spark plug wells.
Spark plug tube seals are small, circular rubber gaskets located inside the valve cover, designed to seal the openings where the spark plugs sit. On engines with an overhead camshaft layout, the spark plug tubes pass through the valvetrain area where oil is continuously sprayed to lubricate the camshafts. The spark plug tube seals prevent this oil from leaking down into the spark plug wells.
Over time, these seals can harden and crack due to engine heat. When they fail, oil leaks into the tubes, submerging the spark plug and the ignition coil boot or spark plug wire. This oil contamination degrades the rubber boot, causing electrical current to arc to the engine block instead of firing the spark plug.
This results in engine misfires, rough idling, poor acceleration, and a flashing check engine light. Replacing these seals is typically done as part of a valve cover gasket replacement service, as the valve cover must be removed to access them.