What will cause my radiator to boil. The temperature gauge stays in the middle. on 2001 Dodge Intrepid

I changed the thermostat.

Asked by for the 2001 Dodge Intrepid
poss bad radiator cap
We check all the hoses and we can't see where it is leaking from. I will check into cap. Thanks
1 more answer , 1 more comment
Finish filling the cooling system, air in cooling system.
I did fill it.