you already have one like that built into your cluster. and im pretty sure thats not based off of water temp

 

The water temp guage is not very accurate in the stock dash. There are also no numbers on it. It is like a WB vs. NB deal. The H2O temp gauge will tell you specifically what the temp is. The stock one usually just goes to operating temp, but what is that?? How close to overheating are you??