Durango 4WD V8-5.9L VIN Z (1998)
Spark Plug: Testing and Inspection
Spark Plug Conditions
Normal Operating
Normal Operation And Cold (Carbon) Fouling
The few deposits present on the spark plug will probably be light tan or slightly gray in color. This is evident with most grades of commercial
gasoline. There will not be evidence of electrode burning. Gap growth will not average more than approximately 0.025 mm (.001 in) per 1600 km
(1000 miles) of operation. Spark plugs that have normal wear can usually be cleaned, have the electrodes filed, have the gap set and then be
installed.
Some fuel refiners in several areas of the United States have introduced a manganese additive (MMT) for unleaded fuel. During combustion, fuel
with MMT causes the entire tip of the spark plug to be coated with a rust colored deposit. This rust color can be misdiagnosed as being caused by
coolant in the combustion chamber. Spark plug performance is not affected by MMT deposits.
Cold Fouling/Carbon Fouling
Cold fouling is sometimes referred to as carbon fouling. The deposits that cause cold fouling are basically carbon. A dry, black deposit on one or
two plugs in a set may be caused by sticking valves or defective spark plug cables. Cold (carbon) fouling of the entire set of spark plugs may be
caused by a clogged air cleaner element or repeated short operating times (short trips).
Wet Fouling Or Gas Fouling
A spark plug coated with excessive wet fuel or oil is wet fouled. In older engines, worn piston rings, leaking valve guide seals or excessive
cylinder wear can cause wet fouling. In new or recently overhauled engines, wet fouling may occur before break-in (normal oil control) is
achieved. This condition can usually be resolved by cleaning and reinstalling the fouled plugs.
Oil Or Ash Encrusted
Oil Or Ash Encrusted
If one or more spark plugs are oil or oil ash encrusted, evaluate engine condition for the cause of oil entry into that particular combustion chamber.
Electrode Gap Bridging
