Anybody have advice for when a spark plug doesn't seem to want to unscrew? I was changing plugs on my newly-bought 87 740. Nos. 1-2-3 came out fine, but #4 next to the firewall moved about an eighth of a turn or less, and got tighter and tighter. Afraid to continue. Tightened it back up and left it. Engine was cold. Would I have better luck with it hot? Aluminum head should expand more that steel base of the plug, maybe?? (Of course, the engine doesn't run very long due to a probable Hall sender problem...) If I end up getting it out and have stripped threads, I know I can re-thread and use an insert (did it once successfully on a Honda, but the cross-engine let me drill straight on, lots of room -- not so on #4 Volvo -- have to pull head, no doubt.)

Is there any hope of a fix as it sits, or am I in for head-pulling? Thanks for any advice, even sympathy...