A spark plug tube seal is a small but essential gasket in an engine, primarily designed to prevent oil leaks into the spark plug tubes.
Specifically, spark plug tube seals go between the engine's spark plug tubes and the engine's valve cover(s) so that engine oil cannot leak from the upper engine area into the spark plug tubes.
Function and Location
In many modern engines, spark plugs are recessed into the cylinder head through tubes. These tubes extend up to the valve cover. The valve cover seals the top of the engine, containing the camshafts and lubricating oil.
The spark plug tube seal acts as a barrier at the point where these spark plug tubes pass through the valve cover. Its primary function is to:
- Prevent Oil Leaks: Stop engine oil circulating within the valve cover area from leaking down into the spark plug tubes.
- Protect Spark Plugs: Keep the spark plug threads and insulator free from oil contamination. Oil can cause misfires or damage to the spark plug and ignition coil.
Why are they Important?
If spark plug tube seals fail or harden over time, engine oil can seep past them and accumulate in the spark plug tubes. This can lead to several issues:
- Engine Misfires: Oil around the spark plug can foul it, preventing a strong spark and causing the cylinder to misfire.
- Ignition Coil Damage: Many modern engines have coil-on-plug ignition systems. Oil can damage the ignition coil that sits directly on top of the spark plug.
- Difficulty Removing Spark Plugs: Oil and debris can make it hard to unscrew spark plugs.
- Smoke: In severe cases, burning oil can produce smoke.
Signs of Failure
Common indicators of failing spark plug tube seals include:
- Oil found on the threads or tip of the spark plug when removed.
- Oil present in the spark plug tubes.
- Engine misfire codes or a rough idle.
- A burning oil smell.
Replacing these seals often involves removing the valve cover, which is a common maintenance task when addressing valve cover gaskets or other top-end engine work.
