Temp Gauge reads car overheating....engine temp. is fine

Change the temp sensor. You pretty much changed everything else already. Also you may want to find another mechanic.

I would make certain that the system is bled properly. A small air pocket around the sensor can have really erratic effects on the "gauge" temperature.

Especially if the sensor is in the very top of a housing, where air may accumulate. Some thermostat housings have a small bleed screw to make this easier.

In general, park the car on a slope such that the front wheels are slightly higher than the rear (driving "uphill').

Remove the radiator cap and leave it off. Set the HVAC temperature to full hot, with a middle fan speed.

Start the vehicle and fill the radiator with the proper coolant mix. Idle the vehicle for a length of time... this could be as much as 30 minutes or more with some vehicles.

Observe the coolant in the neck of the radiator fill. If there are small bubbles bursting, it isn't bled yet. Keep adding coolant mix to keep all radiator fins covered - just below the filler neck.

When the bubbles stop, cap the radiator BEFORE you turn the vehicle off.

Then you can observe your temperature gauge and see if the response has improved. It's a simple process that may not solve your problem, but can't hurt. A properly bled cooling system is essential and a bit of a lost art with some mechanics - especially because it's time consuming and doesn't make them any extra money really.

Good luck!

It's the radiator itself. I went through this with a Ford years ago . It kept overheating and I changed EVERYTHING. Except the radiator. Open the cap and shine flash light into the rsfiatpr. Is there anything that looks like calcium growing I in there, like coral almost ? That build up does not allow the heat to disperse as the water flows throw the radiator. What t o do? If you can ,take it out and break up the deposits inside by hitting the corner of the radiator on the ground. I ve seen that done in a shop. Or just get a new one..

Temp sender unit is faulty: Remove the sender unit wire and earth it against the bodywork and the gauge should go straight up to hot. This indicates that the gauge and wiring is fine and that the sender unit is faulty.