I Have a 2005 S-Type 3.0 , I Have had the Radiator replace, the Thermostat replaced, the water pump replaced, the radiator Reservoir tank and the radiator cap replaced twice and it still doing the same thing it will indicate Hot and then it go's back to normal, don't know what to do next ?

 

How quickly does the indication change? Have you measured the temperature at the crossover pipe (front of the engine) or radiator inlet? An infrared thermometer would give a quick answer. I've got to wonder if you've got an indication problem, not an actual overheat.

If it's an indication problem, the V6 cylinder heat temperature (CHT) sender is very easy to change.

 

agreed , sounds like a sensor or a cluster issue .

if you watch the live OBD temp data also you could see it the temp spike is before the ECM
or at the instrument cluster module ,

 

Oops, from some quick research, it appears only the '99-02 V6 used the CHT sensor. The later V6 (and all years V8) had a coolant temperature sensor. Sorry for any confusion. The problem could still be indication, but from the coolant temperature, not the cylinder head.

Can you please describe exactly when the gauge goes high? Moving on the highway, stopped in traffic, etc.? How high does it go? Does it cool off if you crank the heater to HI? If at idle, does it help to increase the engine RPM? If stopped or moving slowly, does it help to move faster?

One last thought, if a new coolant temperature sensor doesn't help: Have you done a cooling system pressure test? These engines seem to be very finicky about having the proper cooling system pressure. I didn't see any mention of that in your list of work.