A visual inspection of the Spark Plugs will display symptoms and conditions of the engine’s performance.

So, The experienced technician can analyze these Spark Plug symptoms to track down the root cause of many problems.

Always examine the tips of the plugs as they are removed. Hence, This can reveal a great deal about the health and performance of an engine. Consequently, The appearance and color of the deposits can reveal other problems that may need fixing:

  • Normal deposits
  • Fuel fouled spark plug
  • Wet spark plug
  • Oil fouled spark plug
  • Glazed spark plug
  • Damaged plug
  • Overheating
  • Melted electrode
  • Detonation

Spark Plug Replacement

When changing spark plugs, wait until the engine has cooled to remove the plugs. The engine should be at or near room temperature, and not hot to the touch. This is very important with aluminum cylinder heads because it reduces the risk of damaging the threads in the cylinder heads when the plugs come out (aluminum is a much softer metal than cast iron).

Most threads on spark plugs for engines with aluminum heads are either precoated to reduce the risk of thread damage, or the plug shell is made of a nickel alloy. If the plug shell is black or plain steel, however, you should put some antiseize to the threads, and reduce the applied torque by about 30 to 40%.

Do not use antiseize if the plug shell is nickel or has been precoated. Antiseize acts like a lubricant and may allow too much torque to be applied to the plugs, damaging the treads in the cylinder head.

Spark Plugs
Spark Plugs


In Conclusion, Plugs are designed to be self-cleaning up to a point. When the engine is running, the ceramic shell that surrounds the center electrode gets hot and helps to burn off any fuel or oil ash deposits that might otherwise foul the spark plug. Furthermore, The “heat range” of the spark plug determines its operating temperature and its built-in fouling resistance. The plugs should be hot enough to prevent fouling but not so hot that they increase the risk of preignition and detonation.