The electrodes and porcelain of a spark plug can reveal short- and long-term problems if you know where to look. OEMs consider the spark plugs a part of the emissions system on most modern vehicles.

Oil fouling of a spark plug typically results in a shiny, black appearance. If enough oil is in the combustion chamber, the deposits can build up on the tip, porcelain or shell.

If you can’t determine if it is carbon or oil fouling, smell the plug; it will smell like engine oil. The oil can come from the piston rings, valve stem seals or the positive crankcase ventilation (PCV) system.

Malfunctioning PCV systems are becoming a leading cause of oil fouling in modern engines. These systems have become more than just a spring-loaded check valve. Modern systems can separate oil from the crankcase vapors and electronically regulate when the engine ingests the vapors. If the PCV valve is stuck open, the excess vapors and oil droplets can quickly foul the spark plugs.

This video is sponsored by Autolite.