Riviera running hot need help? on 1995 Buick Riviera

My 1995 Buick Riviera starts to run hot after a while of driving it. The water pump is circulating the coolant. The temp on the the dash reads past 200 but does not go all the way to the red mark. What could be the problem? Need help. Also the catalytic converter makes a knocking sound when the car is running but at most times the knocking is silent.

Asked by for the 1995 Buick Riviera
First think I'd check is if radiator fan turning on when gets a little above half on guage. If not may be coolant temp sensor or one or both radiator fan relays. If that doesn't fix jump wires from fan motor directly to battery and see if fan motor out. If working fine replace thermostat. Also look around cylinder head area for any signs of coolant. If there are you may have bad head gasket.