Parts specialist Federal-Mogul has issued some useful tips on how the condition of a spark plug can be an indicator of other issues on a vehicle.

Federal-Mogul is the parent company behind the Champion ignition brand and Regional Marketing Manager, Jonathan Allen says knowing what to look for on a spark plug can help with problem diagnosis. He comments, "A nice greyish white or yellow coloured insulator base is a sign that the engine is in good health with appropriate ignition settings. However, if there are sooty deposits this is generally a sign that an engine is running too rich. The technician should therefore check mixture settings, defective cold start systems and temperature or lambda sensors. It might also be an indication that the plug’s thermal rating is too high or that car is only used for numerous short journeys.”

Plug condition can also be an indicator of potential engine trouble before it develops. An oily residue, for example, is a sign that excess oil is present during ignition, possibly caused by the oil level being too high, or a symptom of worn piston rings, cylinders or valve guides.

Jonathan also points out that melting of either the ground or central electrode can be an indicator that the spark plug is too hot, the air fuel mixture is excessively lean, incorrect ignition advance, a defective exhaust re-circulation system, faulty detonation sensor or a cross induction in the spark plug leads. In extreme cases, it can result in engine damage.

The presence of black burn marks or carbon tracks running vertically down the spark plug insulator toward the shell are caused by current discharge from the top terminal down the outside of the insulator to earth. This is due to a poor fitting or worn spark plug boot and will cause engine misfires, it can be remedied by replacing the affected spark plugs.