Had a stuck plug on number 2 on the 2.2 aluminum head. I knew it was not over torqued since I installed it with never seize and I just snug them up. Not sure what happened but it would unscrew about a quarter a turn and stop. Hit it with PB blaster and slowly worked back and forth with added blaster. Took about an hour letting it sit, working it again and again. It came out and the threads are fine. Just an FYI for anyone this happens to. Don't panic and think the worse. Cold engine, no heat. All the others were fine.