Impreza WRX STI F4-2.5L DOHC Turbo (2007)
3. Oil fouled:
Wet black deposits show oil entrance into combustion chamber through worn rings and pistons or excessive clearance between valve guides and
stems.
4. Overheating:
White or light gray insulator with black or brown spots and bluish burnt electrodes indicates engine overheating. Moreover, the appearance results
from incorrect ignition timing, loose spark plugs, wrong selection of fuel, hotter range plug, etc.