Being a silent(fanless) GPU,you're temps are going to be directly tied to your case temperatures.
Make sure you have atleast 1 exhaust fan and 1 intake fan and the blades are clean and spinning freely.
Additionally,seeing as this GPU model is rather old,the Thermal Paste might be dried up and not conducting heat as well as it used to.
You should purchase a tube of Thermal Grease like
Arctic Silver 5 and get on youtube to watch a tutorial if you're unfamiliar.