Hot coolant temps can be due to any of the following
1 slipping drive belt on the water pump
2 faulty water pump
3 leaking radiator or hoses
4 blocked radiator tubes
5 grass,leaves etc blocking airflow thru the cooling fins
6 faulty thermostat not opening fully
PRO TIP before installing a new thermostat place it in a saucepan and cover with water and place on a stove and see if it actually opens properly as the heat rises.
Absolutely TCJBOLDIE. And you would definitely check all that prior to assuming head gasket.
Been there too many times and sadly working though that list I start stressing out the more and more I get through the list with out a positive diagnosis. Always praying that its not the Head Gasket.