OEM Mercury Monterey Spark Plug

Mercury Monterey Spark Plug Parts and Q&A

• Spark Plug
  AGSF-42F-MX
  Q: How to inspect a spark plug for issues such as bridged gaps, fouling, and overheating on Mercury Monterey?

  A:

  An inspection of the spark plug must focus on visible gap bridging because oil and carbon fouling can create ceramic insulation blockage. Clean the spark plug unless it shows no need for cleaning. A new spark plug installation should only proceed after fixing any oil leak issues and dealing with worn rings and pistons as well as excessive valve-to-guide clearance and worn or loose bearings because excessive oil entering the combustion chamber causes wet black deposits on the insulator shell bore electrodes. Particle fouling is detectable by inspecting black fluffy carbon buildup on insulator tips and shell surfaces and electrodes along with testing the heat range of the plug with air filter state and fuel mixtures and duration of engine operation. Normal operation of the firing tip means it will accumulate light tan or gray materials. Witnesses to pre-ignition can be identified through electrode melting and damaged insulator appearance together with metal residue indicating potential engine damage from improper ignition timing or improper fuel type use or unapproved heli-coil insertion instead of spark plug threads so a new spark plug needs replacement. The combination of engine overheating and wrong fuel type along with loose spark plugs or heat range mismatched plugs or low fuel pressure or improper ignition timing leads to petechial spots and bluish-burnt electrodes. If overheating is observed it requires immediate replacement of the spark plug. The inspection for fused deposits which form as bubbles or blisters following sudden acceleration should prompt cleaning of the spark plug in case of detection.