Normal Worn Plug
A plug displaying normal wear will have
gray/brown deposits and a lightly coated core nose. Gap increased by approximately
0.001" for every 1000 miles driven. These plugs are well suited to the engine
and the engine is in good running condition. |
Carbon Fouled Plug
Plug displays dry black sooty deposits.
Will cause weak spark and eventually misfire. Indicates an overly rich fuel
mixture. |
Oil Fouled Plug
Wet, oily deposits. Will cause weak spark
and eventually misfire. Can be caused by worn bores or piston rings, valve
guides or sometimes (temporarily) during engine break-in period.
|
Overheating
Electrodes have a glazed appearance, core
nose is very white with few deposits. Check plug heat range, ignition timing,
fuel octane rating (too low) and fuel mixture (too weak). Discard plugs
and cure fault immediately. |
Electrode Damage
Electrodes burned away; core nose has
burned, glazed appearance. Caused by pre-ignition. Same checks as for "Overheating"
but may be more severe. Replace plugs and remedy fault before piston or
valve damage occurs. |
Split Core Nose
(May appear initially as a crack) Damage
is self-evident, but cracks will only show after cleaning. Caused by pre-ignition
or improper gap-setting technique. Check ignition timing, cooling system,
fuel octane rating (too low) and fuel mixture (too weak). Discard plugs
and rectify fault. |
