This subject gets beat to death. Been a mechanic for well over 30 years. Never and I repeat Never has even one manufacturer ever used lube of any sort on any spark plug thread ever...
I think there may be more than a few phord owners who wished that phord had used something on their spark plugs.
That was the idiots who thought 2 or 3 threads were plenty to hold a spark plug in....
Ford Engineering at their best :whistling :
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
