overheated

Hey yall! My Nitro was running hot and my mechanic replaced the fan clutch since it was all loose and kinda black. And I drove it last night and then today it got super hot. He checked every hose, nothing is leaking, and all was better after the part. I am wondering if it happened because it was...

My wife came home tonight and said she had no heat and then that the overheat light came on. Do you think this is thermostat related?