cooling water temperature gauge incorrect
 

I have a elantra 2001 GT with the 2.0L engine. just recently the radiator cracked and I lost all the water, I noticed that when the temperature indicator in went into the red area. When I replaced the radiator and drove the car again I noticed the smell of coolant additive all the time, so I plugged my diagnostic tool into it. The coolant temperature was reading way to high and the airconditioning kept switching off, but the temperature gauge was indication a normal running condition and was in the middle. Replacing the thermostat fixed the problem with the car getting hot but it seems like the extreme overheating when the car was without water once damaged something, and it is not the temperature sensor, this one reads correct. Just somehow the gauge doesn't go above the middle position anymore, no matter how hot it gets. But it did it initially and indicated the broken radiator. Does anyone here have any idea how I could fix this problem?