[HotZ28]

Very detailed explanation of the initial problem and subsequent issues! When the 3.1 overheats to a certain point, they usually develop a hairline crack between the combustion chamber & water jacket. When this happens, the pressure test is useless, because the crack expands with combustion heat & the combustion pressure overcomes the coolant pressure; thereby, adding heat to the coolant. You can have the coolant tested for combustion gasses, or you could leave the pressure tester on the radiator until the engine is hot and see if the coolant pressure increases beyond what the cap is rated for. If the pressure increases beyond the cap rating, it will open and divert coolant to the overflow. The coolant temp does not have to be in the red zone for this process to happen, it is simply based on the system pressure. If the coolant gas test proves positive, time to pull the heads. If # 2 plug is wet looking, it sounds this is like the likely culprit. Remember, when you shut the engine off, combustion pressure no longer exist; however, coolant pressure will remain on the system for a period of time, which usually injects coolant into the combustion chamber through the crack, hence the discolored/fouled plug!