I have a 2001 Elantra and just recently the temp gauge has started to act weird. It will get up to operating temp and after a while the needle will drip to 1/4 then to operating temp then at any time drop again. Some says it does it some days not. Any suggestions?

 

Change thermostat even if seems to be good

 

Thermostats do give out , sometimes fully and sometimes intermittent. I believe Josh gave good suggestion.