Iridium spark plug , Toyota Spark Plugs DENSO SC20HR11 OE 90919-01253 For Toyota length 26.5 mm

Overheating
Insulator skirt side was”blach white”shaped electrode ablation prematurely. Because premature ignition timing,cooling system adverse; using a low-grade gasoline, mixture too lean; spark plug into the combustion chamber and spark plug heat value too low; spark plug installation torque is not enough, the outer seal leak worse.

Insulator breakage
End of the spark plug insulator skirt cracking or breakage.The use of low-grade gasoline or cause premature ignition timing.

Oil wet
Hulled face screwed around and luminal surface portion of the insulator and the electrode surface adhesion side skirts with black wet shiny oil.Mainly piston rings, cyclinder wear and tear to because improper carbutetor adjustment

 
Normal operation
End of the spark plug insulator skirt was brown, brown or light gray, electrode erosion is very small, indicating that the spark plugs and the engine is matched
 

Too much coke
Side electrode and insulator attached to a thick layer of yellow skirt powder, is due to the use of leaded fuel additives caused

 
Hot combustion
Melting electrode, the center electrode and the side electrode of the port portion into a molten state. Because premature ignition timing, cooling system adverse; using low-grade gasoline, mixture too lean; spark plug into the combustion chamber and spark plug heat value too low; spark plug installation torque is not enough, the outer seal leak worse

Toner Blackened
Screwed steel face and cavity surface portion of the insulator side skirts and black carbon electrode surface is covered by sediments, causing severe spark plug flameout. Mainly due to the mixture is too thick, clogged air filter, choke improper use; excessive oil consumption, ignition time lag; prolonged low speed and the use of high heat value of the spark plug.

Lead Contamination
Insulator skirt side white powder or yellow,brown, green, and black lead color. Since tetraethyl lead in gasoline at low engine load operation of the skirt adhered to the end surface of the insulator, when the engine speed, high speed, full load operation, the temperature increases further, the spark plug insulator formed on the surface of the conductive lead compound due to temperature increased with the increase, eventually leading to fire the spark plug.

 
Flashover
Porcelain surface axially obvious traces the arc burning sparkle. Is due to prolonged use spark plug electrode burning, the gap is too large, high-voltage insulator jacket poor performance, aging; porcelain high-voltage lines and the gap is too large.
 
 
 
 
 
 
 

Mounting torque is too small
Deformation of the outer washer inadequate leak, resulting in insufficient cooling spark plugs. Spark plug could easily lead to overheating and even pillow melting electrode, porcelain skirt burst.

Corona
On the insulator layer of yellow scale. 2 is due to air under high voltage to 30000 volts is ionized impurities in the air is formed on the insulator attached

 
External damage
Electrode and insulator skirt severely deformed damaged, is due to incorrect use spark plug model, and the impact caused by cylinder