Honda civic 2001 engine temperature acting weird
I recently got a Honda civic 2001 from a friend. The temperature gauge is acting weird. The gauge is staying down to zero for a while and after driving a bit goes to the middle. Then I drops down to zero again (still while driving) and then up and down. Another issue is the car won't start again if still hot. I have to wait for it to cool down before being able to start it again. And it struggles a lot uphill. Coolant is hot after a while. There seems to have a few bubbles when I open the radiator cap while the car is heating. But I already purged and replaced the coolant and waited a while for the bubbles to go. The fan seems to work too.
Coolant color and level seems normal and the oil too.
The engine light is on.
Based on my research it seems to point towards the temps sensor but could there be any other issue.
Any idea on what I should replace first? Thanks for your help.