I have a 2000 Dodge Durango 5.9 4X4 about 50,000 miles on a dodge rebuilt engine, with a problem I cannot seem to isolate. Symptoms are: spark plug in cylinder 7 will foul after 2 months, the plug looks good, its the plugs threads which gets a build up of what looks like a caramelized gas mixture and this goes all the way to the plugs compression ring with some of the material on the compression ring. I have replaced dist. cap and rotor twice, plug wires twice, spark plugs 3 times, Champion Iridium. Compression test, high cylinders around 145 -150
with cylinders 5 & 7 being the lowest at 135. Test preformed 4 revolutions on each cylinder, all plugs out throttle closed. I have tried injector cleaner, no change. I have talked to several local mechanics locally who scratch their heads and say "never heard/saw that before" My fear is that there is a crack in the head at the threads, your thoughts... If you need a photo of the spark plugs, I can provide later today. Thanks in advance Mike Wywias