I have three plugs out of one bank, but one plug is being especially difficult: it's about half way out; I am pouring the PB Blaster to it, but I am afraid it is going to twist off. I would try to warm the head a little to expand the threads, but how to do this if the engine can't run? Maybe pour hot water in the radiator? I think I might get it to go back in; being male, I hate to go "the wrong way", if you understand what I mean.
Once the other three plugs finally came out (with varying degrees of difficulty), the new plugs went right in, threaded in by hand, and were fine.
When we have similar problems with industrial engines, sometimes it is caused by carbon fouling the thread on the end of the plug, then trying to drag back through the other threads during removal. Advice?