If you have the original threaded plug in there, some of them can be quite aggressive. When I rebuilt my engine, the only thing that anyone else removed was that plug. The guy who removed it(before he boiled out the block) said they had quite a struggle with it. I didn't have just the right wrench for it but something close. The threads are fine and probably 8 full threads of engagement. Start soaking with penetrant and heat if you can. Good luck

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.