My 2004 4.2 S-type temp gauge will warm up to middle norm for normal and extended drives, then out of nowhere will start dwindling down to about quarter of gauge, and then, drop almost pegged out on left side of gauge and immediately go to limp mode. Pull off highway, kill engine, wait 30 seconds, restart and needle goes immediately to middle norm(no more limp mode) for the next 50+ miles or maybe not until next trip or next week. Coolant norm, fan works. Has anyone experienced same or have any ideas??????

 

I had opposite.
My car would run 1/4- normal than out of no where jump very quick to hot (like in 2 minutes of driving)
But I had a cracked coolant reservoir....

In your case maybe coolant sensor?

 

Use an OBD tool to monitor ECT (see below) or use ETM and see what temp is doing. Sounds like may be faulty sensor/wiring/connector.