It would depend on the application.
The thermostat is the most likely cause, other than that the temp sensor could have failed sending the wrong temp reading to the gauge.
No
100
100 centigrade
-100
Normal body temp is 98.6 f
100 degrees Celsius
100 degrees Fahrenheit = 37.78 degrees Celsius
212 f, 100 c
100 C
3,150 + 100 k temp _
Inosphere