Spark Plug: Inspection

• Gasoline engine model
  Fig 1: Checking Spark Plug For Abnormalities (Gasoline Engine Model)

  Courtesy of SUBARU OF AMERICA, INC.
• HEV model
  Fig 2: Checking Spark Plug For Abnormalities (HEV Model)

  Courtesy of SUBARU OF AMERICA, INC.

1. Normal:

   Brown to grayish-tan deposits and slight electrode wear indicate correct spark plug heat range.

   Fig 3: Checking Spark Plug Condition - Normal

   Courtesy of SUBARU OF AMERICA, INC.
2. Carbon fouled:

   Dry fluffy carbon deposits on the insulator and electrode are mostly caused by slow-speed driving in town, weak ignition, too rich fuel mixture, etc.

   Fig 4: Checking Spark Plug Condition - Carbon Fouled

   Courtesy of SUBARU OF AMERICA, INC.
3. Oil fouled:

   Wet black deposits show oil entrance into combustion chamber through worn piston rings or increased clearance between valve guides and valve stems.

   Fig 5: Checking Spark Plug Condition - Oil Fouled

   Courtesy of SUBARU OF AMERICA, INC.
4. Overheating:

   A white or light gray insulator with black or brown spots and bluish burnt electrodes indicate engine overheating, wrong selection of fuel, or loose spark plugs.

   Fig 6: Checking Spark Plug Condition - Overheating

   Courtesy of SUBARU OF AMERICA, INC.

Spark plug gap L: 

Standard 

1.0 - 1.1 mm (0.039 - 0.043 in) 

• Gasoline engine model
  Fig 7: Identifying Spark Plug Gap L (Gasoline Engine Model)

  Courtesy of SUBARU OF AMERICA, INC.
• HEV model
  Fig 8: Identifying Spark Plug Gap L (HEV Model)

  Courtesy of SUBARU OF AMERICA, INC.