Do the threads in heads ever strip just from wearing out? That’s what I am being told. My feeling is that the plug was crossed threaded when it was put in or in the case of aluminum heads it was overtightened pulling the threads out. I’m talking about a 4 cyl. 1999 Jetta with 120,000 miles. What’s the opinion out there?
Even if you changed the plugs hundreds of times, if you are careful and follow the torque specification, the threads will never wear out in the lifetime of the car. Threads are damaged in a number of ways; cross-threading, repeated over-torquing and stretching the threads, galling due to corrosion or carbon buildup on exposed threads being backed out of the head.
On my Escape, I think the threads were ruined because I under-torqued the plugs. It ejected a plug. Now it sounds like this caused other problems (that I’m desperately trying to fix).
The torque spec for the Escape is an almost incredible 11 ft-lbs. I’ve never seen a torque spec that low for spark plugs.
So add under-torquing as an additional cause of stripped threads.